Morris Blackburn'sClassroom - UNIT 2 · 2019. 1. 11. · circulatory system. Living Organisms•...

96 MHR • Cells and Systems

• What is light?

• What inventions uselight?

• What do these inventionsreveal about the natureof light?

U N I T 2U N I T 2

Why is a single cell like this one important to allliving things, including you? What is inside acell, and how were scientists able to finally “see”inside one? In Topics 1–3 you will discover whatit means to be alive from ascientific perspective,and you will use amicroscope to seethe “invisible”world of cells.

• What do living organ-isms have in common?

• How are cells organizedto carry out differentfunctions?

• How do systems worktogether to keep organ-isms healthy?

U N I T 2U N I T 2

This girl is doing more than just quenching her thirst. The water she is drinkingis giving all the cells in her body something they need. How do cells usenutrients like water? Does every cell carry out the same functions? Are all cellsthe same? In Topics 4–5 you will find out how cells work and how they areorganized to help organisms carry out their life functions.

Read pages 166-167, Design Your Own

Investigation. Here is a chance to display

your skills in designing controlled experi-

ments. You can start planning your

investigation well in advance …

Start sharing ideas with your teammates.

Save all your ideas in an Experiment

Planning file.

Begin collecting the material you will need

for your experiment.

Think about how you might present your

experimental results in a multimedia

presentation.

Your body is organized intosystems, like the digestive systemshown here. What do differentsystems do? How do they worktogether to keep you alive andhealthy? In Topics 6–7 you willfind the answers to thesequestions, and explore howhealthy lifestyle choices can helpprevent illness and disease in your body.

Unit 2 Preview • MHR 97


T O P I C 1 Living Organisms

Imagine that you are a scientist in the very early days of civilization.You observe all kinds of objects around you, and you begin to wonderabout their similarities and differences. You wonder about the differ-ence between yourself and these objects. You know that you are alive.What does this mean? How many of the objects pictured here are alive,and how do you know?

Movement is one of the signs that something is alive. Is it always asign of life, though? A rock rolling down a hill moves, and it is certain-ly not alive. Perhaps you said that growth is a sign of life (and youwould be correct), but crystals grow. Are they alive?

Living organisms can be found in all shapes and sizes. As different asthey appear to be, they all have much in common. Some of the characteristics of living organisms that scientists agree on are:• living organisms need energy• living organisms respond and adapt to their environment• living organisms reproduce • living organisms grow• living organisms produce wastes

In your Science Log,make a list of character-istics you think areshared by all livingorganisms. Then shareyour list with a group ofclassmates. Make anychanges to your own listbased on the discussion.

Functions and StructuresAll living organisms have to carry out certain functions to stay alive. To carry out these functions, organisms have different structures. 1. Energy: Animals get their energy from their food. What structures

do different animals have to gather and use food? Most plants usethe energy of the Sun to make their own food. What structures doplants have to make food?

2. Environment: Plants need light to make food, so they will bendtoward a light source. What structures in plants enable them tomove in this way? Raccoons feed at night, and deer feed during the day. They both use their eyes to see under very different conditions. In what ways are their eyes similar and different?

3. Reproduction: Living organisms reproduce so that life can continue. A wolf has pups. A watermelon has seeds. Do a wolf and a watermelon reproduce in the same way? What structures enablewolves to reproduce? What plant structures produce seeds?

4. Growth: A dandelion grows from a seed. What structures enable a plant to grow? You grew from a baby to your present size. Whatstructures inside your body enabled you to grow? Why and how doall living organisms grow to the sizes they do?

5. Wastes: Animals get rid of waste gases like carbon dioxide. Theyalso get rid of other wastes through urine and feces. What struc-tures do they have to perform these functions? Plants also give offwastes as gases. What structures help plants do this?

Living Organisms • MHR 99

There are a few plantsthat get some of theirenergy from animals.Sundew plants photosyn-thesize just as otherplants do, but they alsocapture tiny insects withthe sticky droplets ontheir leaves. Nutrientsfrom the rotting insectshelp the plant to grow.

Find OutFunctions and StructuresAll living things must carry out the same functions. How do various organisms carry out their functions, and what structures do they use?

Procedure

1. In your group,choose a function that all organisms carryout, such as getting food for energy. Eachgroup member then chooses a differentorganism (an animal or plant) to find outhow it carries out the function and thestructures it has to do the task.

2. Organize all thefindings to show the comparison betweenthe different organisms. You may uselabelled diagrams, or another organizer ofyour choice. (To review graphic organizers,turn to Skill Focus 2.)

What Did You Find Out?

What general statement can you make aboutthe relationship between structures and theirfunctions?

Performing and Recording

Communication and Teamwork


Levels of Organization in OrganismsIn the previous activity, you probably sawthat organisms have very specialized struc-tures to carry out their various functions.Does this mean that organisms like thoseshown here have nothing in common exceptthese functions?

When scientists study anything, they tryto find the similarities as a way of organiz-ing their knowledge. Over many years ofstudy, they have come to understand thatmost organisms have systems that performcertain functions to keep the organism alive.

Systems are made up of organs. Look atFigure 2.1A. The heart is a major organ ofthe human circulatory system. Which otherorganism shown here has a circulatory system and a heart?

Major organs such as the heart are made from tissues. These aregroups of cells that perform similar functions. The basic unit of everysystem is the cell. For scientists, the cell is the feature that separates allforms of life from non-living things: All living organisms are made upof cells. The cell is the smallest thing that scientists consider to bealive. So the cell is another characteristic, and the most important biologically, that all plants and animals share.

Figure 2.1A The human circulatory system

The circulatory system circulates blood in a human organism.

Specialized musclecells form heart tissue.

Heart tissue made from muscle cells helps your heart beat.

The heart is a major organ of the human circulatory system.

Living Organisms• MHR 101

Figure 2.1B A chipmunk’s digestive system

Figure 2.1C A plant’s shoot system

The main function of the shoot system is to make food for the plant.

The stem is theorgan that keepsthe plant upright.

The tissueprovides support forthe stem.

Specializedcells havethick wallsthat makethe tissuestrong.

The digestive systembreaks down food soit can be used by thechipmunk for energy. Muscle tissue

helps the stomach move so it can breakdown food.

Specialized musclecells form stomachmuscle tissue.

The stomach is a major organ of thedigestive system.

www.school.mcgrawhill.ca/resources/How do scientists find out about plants’ and animals’ characteris-

tics, structures, and life patterns and styles? For information on studies of organisms in Alberta, visit the above web site. Go to Science Resources,then to SCIENCEFOCUS 8 to find out where to go next. Choose a study and

prepare a report or other means of communication to explain thepurpose of the study, its findings so far, and its

final goals.


Cells Work TogetherThe pika is a small relative of therabbit that lives only in the alpineareas of western North America,including Alberta and B.C. Thepika is made of millions of cellsthat work together to help it per-form its various activities. Thecells in the pika’s body — as in allliving organisms — are organizedin particular ways. The habits andenvironment of the animal willoften direct the ways that cells are organized.

For example, pikas eat only plants. Plants are quite hard to digest, sopikas have a special baglike chamber where chewed and semidigestedfood collects. Here, tiny bacteria break down the food and help digestit. The way that a pika uses food differs a lot from the way you usefood. The cells in a pika’s digestive system are organized into differenttissues and organs that help it digest plants. The cells in your body areorganized into tissues and organs that help you digest a large variety of foods.

As you go through this unit you will learn more about how cells areorganized and how they work together to keep organisms alive.

1. Why might a biologist think that the cell is the most important characteristic of living organisms?

2. Name a characteristic of living things shown in each of these examples.(a) a cat purrs when petted(b) a robin eats a worm(c) a plant gives off oxygen(d) a runner sweats after a race

3. How are a dandelion and a deer alike? How are they different?

4. Thinking Critically A biologist from another galaxy might think thatautomobiles are a dominant form of life on planet Earth. Automobilesmove, consume gasoline and oil, and produce wastes. They are shelteredin garages and respond to stimuli. Automobiles age and break down, butnew automobiles appear every year. They evolve, changing in appearancefrom year to year. What arguments would you use to persuade the alienvisitor that cars are not alive?

T O P I C 1 Review

Some animals get toomuch salt and somedon't get enough. Thisseabird ingests saltevery time it eats afish. Its cells cannotfunction properly withall of that salt though,so its body gets rid ofit by concentrating thesalt and releasing itthrough the small tubeon its beak. The cellsof other animals, suchas this moose, needmore salt and they will often find it at salt licks, naturalplaces where salt accumulates.

Microscopes and Cells • MHR 103

T O P I C 2

How do you enlarge something too small to be seenwith the unaided eye? You do it in the same way thatthe student’s face has been enlarged in the photograph.Magnifying an object makes it appear larger.

A World Too Small to SeeThere are living things around you that you cannot see. The human eye can see only objects that are largerthan 0.1 mm. Look at the circles of dots shown below.In the first circle, you can probably see individual dots.In which circle does the colour appear solid? Is thecolour really “solid” or is it, too, made up of dots?Separate dots must be more than 0.1 mm apart in order for most of us to see them.

D

E

F

A

B

C

In this photograph, the student’s face has beenenlarged, or magnified, by the water-filled flask.

Microscopes and Cells

Find OutWhat Does It Take to Enlarge an Object?For how long have people tried to magnifyobjects? Two thousand years ago, earlyRomans used water-filled vessels to magnifyobjects that they were engraving. Test a similarmagnifying technique in this activity.

Materials

bottles, jars, flasks of different shapes, water,textbook

Procedure

1. Fill your containers with water and holdthem in front of a page in your textbook,one at a time.


2. Move each container to different positions— closer to the page, further away, up,down, to the sides — to see if this changeshow the print looks on the page.


1. Which container magnified the print themost? Draw a lens that is in the shape ofthis container.

2. What happened as you moved the containers around?

3. Were the images of the print always right-side up?

Analyzing and Interpreting


Early MicroscopesEarly scientists used their knowledge of magnification to see the invisible world of micro-organisms. One of these was a Dutch linenmerchant named Anton van Leeuwenhoek (1632–1723). His hobby was making magnifying lenses. With his great skill at grinding verysmall lenses, Leeuwenhoek made instruments called microscopes,which magnified objects up to 300 times (300×). Using his simplemicroscopes, Leeuwenhoek studied substances such as blood (see Figure 2.2), pond water, and matter scraped from his teeth. Hebecame the first person to observe organisms made of only one cell. Hecalled these single-celled organisms “animalcules.”

About the same time that Leeuwenhoek was making his observationsin Holland, the English scientist Robert Hooke (1635–1703) wasexperimenting with microscopes he had built, like the one in Figure2.3. Hooke looked through his microscope at a thin piece of cork thathe had cut from the bark of an oak tree. He saw a network of tiny box-like compartments that reminded him of a honeycomb. He describedthese little boxes as cellulae, meaning “little rooms” in Latin. Hooke’sdescriptions have given us our present-day word “cell.”

Cells in All Living ThingsOver the next century, many other scientists used microscopes to

study micro-organisms and to look at different parts of plants and animals. They saw cells in every living thing they examined. In 1839German botanist Matthias Schleiden and zoologist Theodore Schwanncombined their observations. They made the hypothesis that all organisms are composed of cells. A cell is the basic unit of life, theysuggested, because all the functionscarried out by living things are carriedout by their individual cells, as well.

German scientist Rudolf Virchowcontributed his ideas to those ofSchleiden and Schwann. Their ideasformed the basis for a set of hypothesescalled the cell theory. Two importantpoints of this theory that you will learnabout in this unit are:• All living things are composed of one

or more cells.• Cells are the basic units of structure

and function in all organisms.

You will explore more about the celltheory in later studies.

Figure 2.2 Leeuwenhoekwas the first to see redblood cells such as these(160×).

eyepiece

specimen holder

tube

base

Figure 2.3 Hooke’s microscope

Figure 2.4A A compound light microscope

Figure 2.4B A scanning electron microscope (SEM)

Figure 2.4C A transmission electron microscope (TEM)

Figure 2.4D The edge of a razor blade as seen under anelectron microscope.

Microscopes TodayImprovements in technology and designgradually led to the development of moderncompound light microscopes, such as theones in your school. Compound light microscopes have two lenses, which give agreater power of magnification.

The best light microscopes can magnifyobjects as much as 2000×. This is still notenough, though, to see some of the smallerstructures inside cells. For this, scientists useelectron microscopes, which use beams ofelectrons instead of light. The electrons arebounced off the sample, then enlarged toform an image on a television screen or photographic plate. The first electron microscope was built in Germany in 1932. It could magnify up to 4000×.

A Valuable ToolIn 1938, the first practical electron micro-scope was developed by two Canadians at the University of Toronto: James Hillier ofBrampton, Ontario, and Albert Prebus ofEdmonton, Alberta. To test their valuablenew laboratory tool, they first looked at theedge of a razor blade. Under a light micro-scope, the magnified blade edge appeared relatively smooth. Under their electronmicroscope, however, the same edge lookedlike a mountain range of rugged peaks andvalleys. This electron microscope could magnify up to 7000×. Today’s electron microscopes can magnify up to 2 000 000×.

Both light and electron microscopes are used extensively today by scientists, engineers, and medical researchers. Look on page 114 to see some images these micro-scopes can produce.

Your investigations in this unit begin withan introduction to effective microscope use.With these skills, you too will be able toexplore the microscopic world around you.



Using a MicroscopeIn this investigation, you will learn about the different parts of a compound microscope and how to use them. Then you will look at some prepared microscopeslides provided by your teacher. Practise drawing what you observe through themicroscope. In this investigation, you will also find a way to estimate the size ofmicroscopic objects. With these skills, you will later be able to study cells fromplants and animals, and observe live microscopic organisms such as those first seen by Leeuwenhoek.

Part 1

The CompoundLight MicroscopeQuestionWhat are the parts of a microscope?

ProcedureStudy the photograph of thecompound light microscope.Learn the names and func-tions of the different parts of the microscope.

Before going on to Part 2,close your book, and drawand label as many parts ofthe microscope as you can.

2-A2-A

Eyepiece (or ocular lens)The part you look through. It hasa lens that magnifies the object,usually by 10 times (10×). Themagnifying power is engraved on the side of the eyepiece.

TubeHolds the eyepiece and theobjective lenses at the properworking distance from eachother.

Coarse-adjustment knobMoves the tube or stage up ordown to bring the object intofocus. Use it only with the low-power objective lens.

Fine-adjustment knobUse with medium- and high-power magnification to bring the object into sharper focus.

ArmConnects the base and tube.Use this for carrying themicroscope.

Revolving nosepieceRotating disk holds two or more objective lenses. Turn it to change lenses. Each lensclicks into place.

Objective lensesMagnify the object. Each lens has a different power ofmagnification, such as 4×, 10×,and 40×, or 10×, 40×, and100×. The magnifying power isengraved on the side of eachobjective lens. Be sure you canidentify each lens. For example,the low-power objective lens isusually 10×.

StageSupports the microscope slide.Clips hold the slide in position. A hole in the centre of the stageallows the light from the lightsource to pass through the slide.

Condenser lensDirects light to the object being viewed.

DiaphragmUse this to control the amount of light reaching the object being viewed.

Light sourceShining a light through the objectbeing viewed makes it easier tosee the details. (Your microscopemight have a mirror instead of alight. If it does, you will adjust itto direct light through the lenses.)

K

J

I

H

G

F

E

D

C

B

A

S K I L L C H E C K

Initiating and Planning





Eyepiece (or ocular lens)A

TubeB

Coarse-adjustment knobC

Fine-adjustment knobD

ArmERevolving nosepieceF

Objective lensesG

StageHCondenser lensI

DiaphragmJ

Light sourceK

CONTINUED

Parts of a Compound Light Microscope


Part 2

Using Your MicroscopeQuestionWhat is the proper way to use and care for a microscope?

Apparatusmicroscope

prepared microscope slides

Materialslens paper

Safety Precautions

• Be sure your hands are dry whenyou plug in or disconnect thecord of the microscope.

• Handle microscope slidescarefully so that they do notbreak or cause cuts or scratches.

Procedure

Now that you know theparts of the microscope, you are ready to begin usingit. Carry your microscope to your work area. Whencarrying a microscope, holdit firmly by the arm and thebase, using both hands.(a) Position the microscope

at your work area withthe arm toward you. Ifthe microscope has anelectric cord for the light source, make surethe cord is properly con-nected and plugged in.

(b) Use lens paper to cleanthe lenses and the lightsource (or mirror). Donot touch the lenses with your fingers.

(c) Do not turn any knobsuntil you have readthrough the rest of theProcedure.

The microscope shouldalways be left with the low-power objective lens in position. If it is not, rotatethe revolving nosepiece untilthe low-power objective lensclicks into place.(a) Looking from the side,

use the coarse-adjust-ment knob to lower theobjective lens until it isabout 1 cm above thestage.

(b) Look through the eyepiece (ocular lens)and adjust the diaphragmuntil the view is as brightas you can get it.


Place a prepared slide on the stage. Make sure thesample (object to be viewed)is centred over the opening. (a) Look through the

eyepiece and slowly turnthe coarse-adjustmentknob until the sample isin focus.

(b) Use the fine-adjustmentknob to sharpen thefocus.

(c) Adjust the diaphragm toa setting that shows themost detail.

(d) While looking throughthe eyepiece, move theslide a little to the left.Observe in which direc-tion the image moves.Move the slide a littleaway from you and thentoward you. Observewhat happens to theimage.

Find a part of the samplethat interests you and, inyour notebook, sketch whatyou see. Start by drawing acircle to represent the areayou see through your eye-piece. This area is called thefield of view. Make sure thedetails in your drawing fillthe same space in the circleas they do when viewedthrough the microscope.(a) Label your drawing to

identify the sample.(b) Calculate the magnifica-

tion you are using. To dothis, multiply togetherthe magnifying power ofthe objective lens andthe magnifying power ofthe eyepiece lens.Record this result onyour drawing. Example:A 10× eyepiece and a 4×objective give a totalmagnification of 40×.

To see more details, rotatethe revolving nosepiece tothe next objective lens. Donot change the focus first.After the medium-powerobjective lens has clickedinto place, adjust the focususing only the fine-adjust-ment knob.

Do not use thecoarse-adjustment knob withthe medium- or high-powerobjective lens.(a) When you have finished

viewing and drawing thesample, remove the slideand return it to theproper container.

(b) If you do not continue toPart 3, carefully unplugthe microscope andreturn it to the storagearea.

CAUTION

CONTINUED

Stageclips holdthe slidein place.

To learn how to make accurate scientific drawings, turn to Skill Focus 11.


Part 3

Measuring the Field of View

QuestionHow can the actual size of a microscopic object be determined?

Apparatusmicroscope

prepared microscope slides

transparent plastic ruler

Materialslens paper

Procedure

Set your microscope to thelow-power objective andplace a clear plastic ruler onthe stage.

Focus on the ruler and moveit so that one of the centi-metre markings is at the leftedge of the field of view.

Measure and record thediameter of the field of viewin millimetres (mm).Millimetre markings on theruler are too far apart to permit direct measurementof the field of view for lenseswith magnification higherthan 10×. You can, however,calculate the field of view fora higher magnification. Tofind out how to do this, goto “How to Calculate theField of View” on the fol-lowing page.(a) Unplug the microscope

by pulling out the plug.Never tug on the electri-cal cord to unplug it.

The diameter of the field of view illustrated here is 2.5 mm.

plastic rulermillimetremarkings


Analyze1. How many lenses does the light pass through

between the light source and your eye?Name them.

2. The coarse-adjustment knob is used onlywith which objective lens? Explain why.

3. How can you tell which objective lens is inthe viewing position?

4. When you move a slide on the microscopestage away from you, in what direction doesthe object seen through the eyepiece move?

5. Make a table with two columns like the oneshown here. Give your table a title. In thefirst column, list the parts of a microscope. In the second column, record the function of each part.

Conclude and Apply6. Why should you never allow an objective

lens to touch the slide?

7. Calculate the magnifying power of yourschool microscope when you use:(a) the medium-power objective lens (b) the high-power objective lens

8. Use your measurement in question 7, part (a)to calculate the diameter of the field of viewunder high power (in mm).

9. Why is the field of view under high-powermagnification less than that under low-powermagnification?

Function of microscope partMicroscope partIf you need to review units of measurement in the metricsystem, turn to Skill Focus 4.

Scientists measure thesize of cells in unitscalled micrometres (µm);1000 µm = 1 mm. If youknow that your field ofview (its diameter) underan objective lens is2.5 mm, how manymicrometres is its diameter? If two cells ofequal size occupy theentire field of view, whatis the diameter of eachcell in micrometres?

How to Calculate the Field of ViewIf you know the diameter of the field of view for the low-power lens, you can calculate the field of view for the other lenses. Use the following formula to do this.

Medium-power = Low-power × Magnification of field of view field of view low-power objective lens______________________

Magnification of medium-power objective lens

If, for example, your low-power objective lens is a 4× lens with afield of view of 4 mm, and your medium-power objective lens is a10× lens, then your calculations would be:

Medium-power= 4 mm × 4field of view

__10

= 4 mm × 0.4= 1.6 mm

Do a similar calculation to determine your high-power field of view.Record this value.


Preparing a Wet MountNow that you have learned how to use a microscope properly, you are readyto prepare some slides of your own, using a variety of materials.

QuestionHow is a sample prepared on a microscope slide?

Safety Precautions

• Be careful when using sharpobjects such as tweezers andscissors.

• Handle microscope slides andcover slips carefully so that theydo not break and cause cuts orscratches.

Apparatusmicroscope

microscope slides

cover slips

medicine dropper

tweezers

scissors

Materialssmall piece of newspaper

tap water

other samples

lens paper

Procedure

Cut out a small piece ofnewspaper containing a sin-gle letter. Use an e, f, g, s, orh. Pick up the letter with thetweezers and place it in thecentre of a clean slide. Note:Always use clean slides andcover slips. Wash the slideswith water and dry themcarefully with lens paperwhen you have finished.

Use the dropper to place avery small drop of tap wateron the newspaper sample.Then, hold a cover slip gently by its edges and placeit at an angle of 45° on thesurface of the slide. Note:Always hold microscopeslides and cover slips by theedges to avoid fingerprints.

Slowly and carefully lowerthe cover slip over the sam-ple. Make sure there are noair bubbles trapped under-neath the cover slip. Thistype of sample preparation is called a wet mount.

2-B2-B

S K I L L C H E C K





Troubleshooting• Do you see round or oval shapes on the slide? These are

likely to be air bubbles. Move the cover slip gently with your finger to get rid of them, or study another area of the slide.

• Do moving lines and specks float across the slide? They are probably structures in the fluid of your eyeball that you see when you move your eyes. Don’t worry; this is natural.

• Do you see a jagged line? This could be a broken cover slip.

• Always place the part of the slide you are interested in at the centre of the field of view before changing to a higher-power objective lens. The drawing on the right shows a view under low power. When you turn to medium and high power, you may not see A and parts of C. Why not?

• Do you close one eye while you look through the microscope with the other eye? You might try keeping both eyes open. This will help prevent eye fatigue. It also lets you sketch an object while you are looking at it.


Set your microscope to thelow-power objective lens.Place the slide with the letteron the microscope stage.(a) Look through the

eyepiece and move theslide until you can seethe letter. Adjust thecoarse-adjustment knobuntil the letter is in focus.

(b) Move the slide until youcan see the torn edge ofthe piece of newspaper.Slowly turn the fine-adjustment knob aboutone-eighth turn eitherway. Observe if thewhole view is in sharpfocus at one time.

Analyze1. When scanning a microscope slide to find an object, would

you use low, medium, or high power? Why?

2. Before rotating the nosepiece to a higher magnification, it isbest to have the object you are examining at the centre of thefield of view. Why?

3. To view the letter e through your microscope the right wayup, how would you position the slide on the stage?

4. A student has made a wet mount of a piece of newspaper butsees several clear, round shapes in the field of view. Whatmight these be? How could the student avoid having themappear on the slide?

Extend Your Skills5. Prepare and examine microscope slides of different samples

of materials, such as strands of hair, cotton, Velcro™, andgrains of salt or sand. Obtain your teacher’s approval of thematerial you select.

A B

C


1. In a compound light microscope, what is the function of (a) the eyepiece(b) the coarse-adjustment knob(c) the stage(d) the diaphragm

2. (a) What is a wet mount?(b) How do you prepare a wet mount?

3. (a) Who first observed single-celled organisms?(b) What did this scientist call them?

4. Who was the first scientist to use the term “cell”?

5. Thinking Critically Why was the development of the microscopeimportant to the study of cells?

T O P I C 2 Review

Modern electron microscopes can magnify objects2 000 000×. The image can be viewed on a televisionscreen. However, it is usually photographed. The resultingimage is known as an electron micrograph.

There are two main types of electron microscopes. In atransmission electron microscope (TEM), electrons arepassed through very thin sections of a sample. Besidesbeing sliced very thin, the object has to be placed in a vacuum. There is no air in a vacuum. Thus, only dead cells and tissues can be observed with a TEM. A scanning

electron microscope (SEM) is used to observe the surfacesof whole objects. With a SEM, you can view and photographliving cells. In this type of electron microscope, electrons arereflected back from the surface of the sample, producingthree-dimensional images.

Electron microscopes have helped scientists understandmany microscopic structures such as the parts of a cell. The image on the left below was produced by a transmissionelectron microscope, while that on the right was producedby a scanning electron microscope.

B Scanning electron microscopes show great detail onthe surface of an organism. This is a tiny dust mitemagnified 350×.

A This micrograph of a thin slice of a dust mite wastaken by a transmission electron microscope.

The Cell and Its Structures • MHR 115

T O P I C 3 The Cell and Its StructuresStrange as it might seem, a cell in your finger has characteristics in common with a microscopic organism and with the cells in an oak leaf.One way to understand the structure and function of cells in multicel-lular (many-celled) organisms, such as human beings, is to investigatethe characteristics of unicellular (single-celled) organisms, like theones shown in Figure 2.5.

The photographs in Figure 2.5 show a variety of microscopic pondorganisms. Although each organism consists of only one cell, they arenot simple. Each has a way of moving, obtaining food, and carrying outall other functions essential for life.

In what ways do youthink a human home may be like a cell? Writeyour ideas in yourScience Log.

Figure 2.5

Diatoms (100x) Varied in shape and beautiful.Diatoms produce shells around themselves,make their own food through photosynthesis,and are free-floating.

Paramecium (160x) Paramecia obtain theirown food from the external environment. Theyare covered with short, hairlike structurescalled cilia that are used both for movementand to sweep food into a tiny groove that issimilar to a mouth.

Euglena (100x) A common pond organismthat also photosynthesizes, and moves bymeans of a single flagellum.

Volvox (30x) Living balls made of manyvolvox live together as a colony. Each has itsown flagellum and makes its own food byphotosynthesizing.

Stentor (125x) Stentor and some otherunicellular organisms produce stalks toattach themselves to the bottom of pondsand streams. Stentor, like paramecium, hascilia, but these structures are used to bring infood rather than for movement.

Chlamydomonas (180x) Makes its own foodthrough photosynthesis, and moves by meansof two long, whiplike structures called flagella.


Pond Water SafariIn this investigation, you will observe and draw various micro-organisms found inpond water. Some of these tiny organisms are like animals, some are like plants.They move and feed in different ways. You will record which characteristics of living organisms you observe in unicellular organisms. You will probably also seesmall organisms made of more than one cell in the pond water you observe.

QuestionHow do unicellular organisms meet their basic life needs?

Pull two or three cottonfibres from the cotton fabric and place them on the water drop.

Place a cover slip on thesample.

Examine the slide under lowpower, looking for differentunicellular organisms.(a) Draw several different

organisms, putting in asmuch detail as you canobserve. Try to identifythe organisms from thephotographs in Figure2.5 on page 115.

(b) Record which character-istics of living organismsyou observe in unicellu-lar pond organisms.

(c) Wash your hands afterthis investigation.

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Safety Precautions

• Be careful when using sharpobjects such as tweezers.

• Dispose of materials according toyour teacher’s instructions.

Apparatus microscope

microscope slides

cover slips

medicine dropper

tweezers

Materialspond water

cotton fabric

Procedure

Obtain a sample of pondwater from your teacher.Using a medicine dropper,place a drop of the pondwater in the centre of a cleanmicroscope slide.

Looking Ahead

Make a list of thingsthat caused a responsein the micro-organismsyou saw. Add to the listas you work more withcells. You could useyour list in the UnitInvestigation,Responding toChanges.


Analyze1. Suggest why you were asked to add

cotton fibres to the water drop.

2. Describe what evidence you saw that shows unicellular organisms are able to feed. Recall that organisms may feed byingestion — taking in substances, or by photosynthesis — producing food themselves (using energy from sunlight).

Conclude and Apply3. What methods of movement did

you observe?

4. Describe any evidence of growth or reproduction you saw.

5. Do unicellular organisms respond to stimuli(changes in their environment)? Explain.

Extend Your Knowledge6. If you also observed multicellular organisms,

describe how they differ in general from unicellular organisms. How are they similarto unicellular organisms?

Extend Your Skills7. Keep a sample of pond water in a safe place

exposed to sunlight for about a week beforereturning it to the pond. Use a microscope to observe the microscopic life in the waterevery day or two. Record any changes yousee. Suggest an explanation for these changes.

In your pond water sample, look for the amoeba, anothercommon unicellular organism shown in the introduction tothis unit. You might be fortunate enough to observe anamoeba in action. The amoeba moves by changing itsshape. It pushes its cytoplasm against one part of its cellmembrane, causing a bulge. This bulge is called a false foot

(pseudopod). Then the amoeba shifts the rest of itscytoplasm in the same direction. The amoeba’s ability to“flow” from place to place using its false feet also allows itto obtain food. The amoeba simply moves around a smallerorganism such as a bacterium, trapping it inside a foodvacuole.

bacterium

nucleus (controls most of thecell’s activities)

false feetamoeba

cell membrane(surrounds andprotects the cell’scontents) cytoplasm

(jellylikematerial inwhich otherparts of thecell float)

food vacuole(stores fooduntil it is used)


Observing Plant and Animal CellsYou are now ready to begin observing the cells of multicellular organisms. Whenyou first look at the cells of a plant or an animal through a microscope, they maylook like rows of squashed boxes stacked together. There may appear to be little ornothing inside them. To observe the parts of a cell more clearly, scientists usuallyadd coloured stains of various kinds to help.

In this investigation, you will continue to develop your skills using a microscopeto investigate cells. You will prepare a wet mount of onion skin cells and look at aprepared slide of human skin cells.

QuestionWhat do plant and animal cells look like through a microscope?

Part 1

Observing Plant CellsSafety Precautions

• Onion juice may sting your eyes.Wash your hands after handlingthe onion.

• Iodine solution may stain your hands or clothes. Avoidspilling it.

• Be careful when using sharpobjects such as tweezers.

• Handle microscope slides andcover slips with care so they donot break.

If you get iodine on yourskin or in your eye, inform yourteacher and rinse the affected areawith water. The eye should berinsed for at least 15 min — iodineis an irritant and is toxic.

Apparatusmicroscope

microscope slides

cover slips

medicine dropper

tweezers

Procedure

Use tweezers to peel a single, thin layer from theinner side of a section ofonion. If you cannot seelight through your onionskin sample, try again.

CAUTION

Materialssmall piece of onion

tap water

dilute iodine solution

lens paper

Carefully place your onionskin sample in the centre ofa clean slide. Make sure theonion skin does not foldover.

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Add a small drop of water.Place a cover slip over thesample.(a) Examine the onion skin

sample using the low-power objective lens onyour microscope.

(b) Move the slide until youlocate a group of cellsthat you wish to study.Centre these cells inyour field of view anddraw what you see.

Prepare another wet mountof the onion skin cells. Thistime, use a small drop ofdilute iodine solution insteadof water.(a) Examine the stained

cells, first using the low-power objective lens andthen the medium-power objective lens.

(b) Carefully rotate the nosepiece to the high-power objective lens.Focus on the cells usingthe fine-adjustmentknob.

Draw what you see and label your diagram.(Hint: Observe if anyparts are similar to theparts of an amoebashown on page 117.)

(c) Dispose of the onionmaterial, clean yourslides, and wash yourhands. Set the micro-scope to the low-powerobjective lens.

CONTINUED

An onion skin sample viewed througha compound light microscope (100×).The skin of an onion is made up of acollection of cells.


Part 2

Observing Animal CellsApparatusmicroscope

prepared slide of human skin cells

Materialslens paper

Procedure

Examine a prepared slide of human skin cells underdifferent magnifications.Draw what you see and label your diagrams.

Clean your slide with lenspaper, set the microscope tothe low-power objectivelens, and put the microscopeaway. Then wash yourhands.

Analyze1. How was your study of cells affected by

(a) using high-power magnification(b) adjusting the light(c) staining the cells

2. List any differences and similarities you observed betweenonion skin cells and human skin cells. Make a comparisonchart to summarize the differences and similarities.

Conclude and Apply3. One function of skin is to protect and support the parts

underneath it. How might the structure and arrangement ofcells in the onion skin help do this?

4. Thinking Critically Why do you think plant and animalcells have different structures?

Human skin cells (250×).

cytoplasm

cellmembrane

nucleus


Cell Parts Viewed With a Light MicroscopeWith your compound light microscope, you have been able to see thebasic cell parts in unicellular organisms and in typical animal and plantcells. The cells of multicellular organisms fit together in much thesame way as a building made of bricks (see Figure 2.6).

The cheek cells scraped from the inside of a person’s mouth shownin Figure 2.7 again show you the major parts of an animal cell youshould be able to see under a compound light microscope. Likewise,the cells scraped from the surface of a leaf (see Figure 2.8) show themajor parts of a plant cell you should be able to see with your ownmicroscope. Next, you will learn more about these cell parts and whatthey do to keep each and every cell alive and functioning.

Figure 2.6 Cells fit togethermuch like bricks in a wall.

cytoplasm(jellylike materialin which otherparts of the cellfloat)

cell membrane(surrounds the celland protects thecell’s contents)

cell wall(thick coveringoutside the cellmembrane)

nucleus(controls most ofthe cell’sactivities)

vacuole(liquid-filled partfor storage;smaller andfewer in animalcells)

chloroplast(contains thegreen pigment,chlorophyll)

Figure 2.8 Colour-enhanced image of a typicalplant cell magnified 250×.Colour enhancement makesthe chloroplasts appear redrather than green.

Figure 2.7 Colour-enhanced image of a typicalanimal cell magnified 250×.

Cell PartsEvery cell must carry out certain activities that keep it alive. Theseactivities include obtaining materials and supplies of energy, makingproducts, and getting rid of wastes. To carry out these functions, cellshave some basic structures in common. Structures inside the cell areknown as organelles. Each organelle has a role to play in the activitiesnecessary for life. Many of the details of cell organelles have only beendiscovered since the invention of the electron microscope. Look closelyat the diagrams on these two pages to see which organelles are found inboth plant and animal cells. Which parts are found only in plant cells?How do these diagrams compare with the images on page 121?

A

B

C

Animal Cell

D

Cell membraneLike the skin covering your body, the cell membranesurrounds and protects the contents of the cell. Thecell membrane is not simply a container, however. Itsstructure helps control the movement of substances inand out of the cell.

CytoplasmA large part of the inside of the cell is taken up by thejellylike cytoplasm. Like the blood flowing throughoutyour body, cytoplasm constantly moves inside the cell.The cytoplasm distributes materials such as oxygen

and food to different parts of the cell. The cytoplasmalso helps support all the other parts inside the cell.

NucleusA large, dark, round nucleus is often the most easilyseen structure in a cell. The nucleus controls the cell’sactivities. It contains the chromosomes — structuresmade of genetic material that direct a cell’s growth andreproduction. The cell nucleus is enclosed by a nuclearmembrane, which controls what enters and leaves thenucleus.

C

B

A

Because cells do work,they need energy. Theirenergy is produced byoval-shaped organellescalled mitochondria (sin-gular: mitochondrion).Inside the mitochondria,tiny food particles arebroken down to releasetheir chemical energy for the cell’s activities.Some cells, such asmuscle cells, have moremitochondria than othersbecause they need moreenergy to function.


Plant Cell

VacuolesBalloonlike spaces within the cytoplasm are storageplaces for surplus food, wastes, and other substancesthat the cell cannot use right away. These structures,called vacuoles, are surrounded by a membrane.

Cell wallThe cell wall occurs only in the cells of plants andfungi, and in some unicellular organisms. Cell walls aremuch thicker and more rigid than cell membranes,and are made mostly of a tough material calledcellulose. They provide support for the cell.

ChloroplastsChloroplasts are the structures in which the processof photosynthesis takes place. Photosynthesis usesenergy from the Sun to make carbohydrates. Foldedmembranes inside each chloroplast contain the greenpigment chlorophyll, which absorbs sunlight.

Chloroplasts are found only inside cells in greenplants and in some unicellular organisms. They are not found in animal cells.

F

E

D

D

A

B

C

E

F A tree consists mainly ofdead cells. The strengthand rigidity of woodcome from the cell walls.These cell walls remainstacked together solidlylike bricks, long after thecells have ceased to carry out their livingfunctions. The only livingparts of a tree are theleaves, the growing tipsof branches and roots, athin layer of cells justunder the bark, and thepith in the centre of theroots and the branches.

The structures thatRobert Hooke saw in apiece of bark were notliving cells at all, but onlythe cell walls of dead,empty plant cells.



Build Your Own 3-D CellMaking a three-dimensional model of a cell will help you remember all the different parts of a cell and how they fit together.

ChallengeDesign and build a three-dimensional model of acell that features the organelles a cell needs inorder to function.

Safety Precautions• Never eat or drink anything in the science

laboratory.• Wash your hands after completing this activity.

MaterialsEveryday items of your choice, for example,gelatin, modelling clay, shoe box, StyrofoamTM, pipe-cleaners, plastic film, hard candies, dried pasta, craft items, etc.

Design SpecificationsA. Your model cell may be either a plant cell or

an animal cell.

B. The organelles needed for the cell to functionmust be present.

C. Your model cell must contain all the rightparts in the right proportions, and the partsmust be clearly visible. It should be no largerthan a shoe box or a basketball.

Plan and Construct With your group, decide whether to build aplant cell or an animal cell.

List the organelles that your cell needs inorder to function.

Decide which materials would best representyour cell and each organelle in your cell.Write each item beside the matching organellein the list of organelles you made in step 2.

Make a neat labelled sketch of your design.Make sure you include and label all theorganelles.

Start building your cell!

EvaluateWork together to examine and compare the modelcells constructed by the various groups. In whatway or ways could you modify your design toimprove it?

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www.school.mcgrawhill.ca/resources/

Do you want to take an imaginary journey through acell? Go to the above web site, then to Science Resources,and on to SCIENCEFOCUS 8 to find out where to go next.

You can zoom in, turn around, and check out different organelles inside a virtual cell.


Cell Size and FunctionWhy are cells so small? Why aren’t largerorganisms, such as the trees in Figure 2.9,made from one large cell instead of millions of microscopic cells? The explanation of whycells do not grow very large can be found inhow cells function.

To carry out their work, cells need a constant supply of materials such as oxygen,water, and food particles. They also need toget rid of waste products. A larger cell wouldneed more materials and would produce morewaste products. However, the only way formaterials to get in and out of the cell isthrough the cell membrane.

To have an idea of the problem this causes, imagine the cell as a round swimmingpool with a diameter of 50 m. To keep thisimaginary cell alive, you must swim to thecentre of the pool carrying a beach ball (representing food particles), then swim backto the side carrying a lifebuoy (representingwaste products). Suppose you must do thistwelve times in a certain period of time.What differences would it make if the diameter of the pool were 100 m instead of 50 m? Figure 2.9 Why are all large organisms, including you,

multicellular?

A single cell may contain many thousands of organelles. Ifthe cell were the size of a large building, such as a school,the organelles would range in size from beachballs toclassrooms.

Each organelle has a characteristic structure, and carriesout the same function in every cell where it is found. Howmight the organelles of a cell be compared with theorgans of your body, such as the stomach, lungs, andbrain? In your Science Log, list some organelles. Besideeach one, write what body organ they appear to be mostlike and why. Try this now, then after you have completedTopic 6, check to see if you would like to change any ofyour comparisons.

Small, Smaller, SmallestCells come in a variety of sizes and shapes. Most cells, however, fallinto a narrow range of size — the size in which they function most efficiently. To grow bigger, organisms add more cells to their bodiesrather than growing bigger cells. This occurs when cells divide.

Recall that cells are measured in micrometres (µm). Most cells inplants and animals have a diameter between 10–50 µm (see the examples in Figure 2.10). Bacterial cells are much smaller. They areonly 1–5 µm across.

Figure 2.10 Relative sizes of a plant cell, animal cell, and bacterial cell

1. Give two examples each of (a) a unicellular organism, and (b) a multicellular organism.

2. List three key differences between a unicellular organism and a multicellular organism.

3. Describe two characteristics of life you have observed in a unicellularorganism.

4. From your observations, list two structures that all cells seem to have incommon.

5. Why might scientists add stains to cells they view under microscopes?

6. Name two structures in a plant cell that are not found in an animal cell.

7. Do organisms grow larger by (a) increasing the size of their cells, or (b)adding more cells? Explain your answer.

8. Thinking Critically Why would you not expect to see chloroplasts incells from an onion root?

T O P I C 3 Review


The Art of Science

Many people with a pas-sion for both art and science combine them tobecome scientific illustra-tors. Besides an eye forfine detail, most scientificillustrators have a degreeor a diploma from an artcollege, as well as a university degree in a specific area of science.

Take a look at a few ofthe scientific illustrationsin this unit. Which schoolsubjects do you thinkwould be important if youwere planning to work inthis field? What are someoutside-school intereststhat might be useful? Youcan start thinking nowabout the types of draw-ings to include in yourportfolio, if you think youmight like to become ascientific illustrator.

Wrap-up Topics 1–3 • MHR 127

T O P I C S 1 – 3Wrap-up

If you need to check an item, Topic numbers are provided in brackets below.

Key Termscellmagnifymicroscopeswet mount

multicellularunicellularorganellescell membrane

cytoplasmnucleusvacuolescell wall

cellulosechloroplasts

Reviewing Key Terms1. In your notebook, match the description in column A with the correct term

in column B.

• carries out photosynthesis in plant cells

• gives plant cells strength and support

• a moving fluid that distributes materials

• controls the cell’s activities

• a thin, protective “skin”

• stores materials

• nucleus (3)

• cell membrane (3)

• chloroplast (3)

• cytoplasm (3)

• vacuole (3)

• cell wall (3)

BA

2. Is an earthworm unicellular or multicellular?Explain your answer. (3)

3. Describe two differences between the cell membrane and the cell wall. (3)

Understanding Key Ideas4. List three characteristics of living

organisms. (1)

5. How were cells first discovered? (2)

6. Copy the different parts of a microscope listed below in your notebook and describe the function of each part. (2)(a) ocular lens(b) tube(c) coarse-adjustment knob(d) fine-adjustment knob(e) arm( f ) revolving nosepiece(g) objective lenses(h) stage(i) condenser lens

(j) diaphram(k) light source

7. Where would you find the substance chlorophyll in a cell? What is its function? (3)

8. Which of the following would you expect tofind in an animal cell? Give a reason for eachanswer. (3)(a) nucleus(b) chloroplast(c) vacuole

9. Explain why cells are limited in size. (3)

10. Copy the diagram of a cell shown below andlabel the cell parts that you know. (3)


T O P I C 4 Fluid Movement in CellsThe Cell MembraneHow long could you live without drinking? Without breathing?Without eating? These everyday activities are essential for life, but whydo we need to drink, breathe, and eat? There are many ways to answerthis question. One way is to look at these essential life functions at thelevel of cells.

Individual cells carry out the same activities as whole organisms.When you drink water, the water is eventually used by your cells, helping them to carry out their functions. Similarly, your cells alsomake use of the air you breathe and the food you eat. In this Topic, you will learn about some of the ways in which cells function.

At the border separating two nations, customs officers check theitems that travellers are carrying. It is against the law to transport certain items across international borders. In a similar way, materials

passing into and out of a cell are “checked” at thecell membrane. Like the customs checkpoint, acell membrane allows some substances to enteror leave the cell, and it stops other substances.Because it allows only certain materials to crossit, the cell membrane is said to be selectivelypermeable. (A membrane that lets all materialscross it is permeable. A membrane that letsnothing cross it is impermeable.)

How does a cell membrane carry out this func-tion? The answer is in the structure of the membrane. Imagine youhave two small bags. One is made of plastic, the other of cheesecloth.Now imagine you pour water into both bags, as shown in Figures2.11A and B. The plastic holds the water, but the cheesecloth lets thewater run through. The plastic is impermeable to water, while thecheesecloth is permeable to water. This difference is due to differencesin the structure of the materials from which the bags are made.

Figure 2.11A Plastic is impermeable to water. Figure 2.11B Cheesecloth is permeable to water.

How do you think cellsmanage such functions as“breathing” and “eating”?List or sketch your ideasin your Science Log. Lookback on your ideas afteryou have finished thisTopic.

Now imagine you are pouring a mixture of water and sand into bothbags. Is each bag permeable, impermeable, or selectively permeable to the mixture? (If you are not sure, you could try carrying out ademonstration like the one in Figures 2.11A and B and observing what happens.)

DiffusionThe structure of the cell membrane controls what can move into and out of a cell. What causes substances to move in the first place?One clue is shown in Figure 2.12. What makes the blob of ink moveoutwards through the water in the container?

Figure 2.12 In time, the ink particles will become evenly dispersed with the water particles,and the whole solution will appear ink-coloured.

Our understanding of particle movement is expressed in the particlemodel. It describes the constant movement of particles in all liquidsand gases. These particles move in all directions, bumping into eachother. (To review the particle model, see page 72.) These collisionsexplain why particles that are concentrated in one area, such as the inkblob, spread apart into areas where there are fewer ink particles, andthus fewer collisions. This spreading-out process is called diffusion.Eventually, the ink particles will become evenly distributed throughoutthe container of water. At this time, individual ink particles continue tomove, but there is no further change in the overall distribution of theink in the water. Just like the ink, food colouring and the colour fromcertain crystals would also diffuse throughout the water, if left undis-turbed for several minutes.

Fluid Movement in Cells • MHR 129

Here are some situationsin which diffusion occurs:a sugar cube is left in abeaker of water for awhile; fumes of perfumerise from the bottle whenthe top is removed. Givesome other examples ofdiffusion. Can solids dif-fuse? Why or why not?Write your responses inyour Science Log.

Recall that an average cell has a diameter of 20–30 µm. Supposethis cell was placed in a solution with a concentration of oxygenhigher than in the cell’s cytoplasm. The time required for diffusion

to equalize the concentrations would be about 3 s at room temperature. If the cell were muchlarger — with a diameter of 20 cm, say — the same process would take about 11 years!

You can observe diffu-sion by means of yoursense of sight. Is thereanother way to observethis process? Try this.Have a friend or a familymember stand at one endof a room with an orangewhile you stand at theother end facing the wall.Ask your friend to peelthe orange. How do youknow that particles havediffused from the orangethroughout the air in theroom? Does the processof diffusion in air workthe same way it does in water?


Diffusion in CellsDiffusion also plays a part in moving substances into and out of cells.For example, imagine an amoeba living in water. The concentration ofdissolved carbon dioxide gas in the water is the same as the concentra-tion of dissolved carbon dioxide gas in the amoeba’s cytoplasm. Carbondioxide particles therefore move into and out of the cell at the samerate, passing through small openings in the amoeba’s selectively permeable membrane (see Figure 2.13A).

Now imagine the amoeba has been producing carbon dioxide as awaste product inside its single cell. The concentration of dissolved car-bon dioxide particles in the amoeba’s cytoplasm is now greater than theconcentration of carbon dioxide in the surrounding water. As a result,more carbon dioxide particles move out of the cell by diffusion duringa given time than move into the cell (see Figure 2.13B). The diffusionprocess continues until the concentration of the dissolved carbon dioxide gas on both sides of the cell membrane is once again equal.

OsmosisThe most common substance found inside and around cells is water.About 70 percent of a cell’s content is water, and most cells die quicklywithout a supply of this liquid. Water particles are small and can easilymove into and out of cells by diffusion. The diffusion of water througha selectively permeable membrane is called osmosis.

You have probably already seen osmosis at work. Have you ever cutcarrot sticks from a fresh carrot? You may have left some extra sticks inthe refrigerator. By the next day, they have lost some of their moistureand they have gone limp. Suppose you place the sticks in a glass ofwater. Several hours later they are crisp again. What has happened?Water particles have moved from the water in the glass into the carrotcells by osmosis. (See Figures 2.14A and B.)

Figure 2.13A An equal concentration of carbon dioxide particles on both sides of the cell membrane. The particles move intoand out of the cell at an equal rate.

Figure 2.13B A greater concentration ofcarbon dioxide particles inside the cell. Theparticles move out of the cell at a greater ratethan they move into the cell.

Can your doctor give youmedicine without usingpills, syrups, or needles?Yes, by using diffusion.Drugs can be put into apatch similar to a Band-Aid™ that is stuck ontothe skin. There is a highconcentration of drugs in the patch but a lowconcentration in thebody. Therefore, the drug particles diffusethrough the skin into thebloodstream.

Figure 2.14A Limp carrot sticks

Figure 2.14BCarrot sticks 24 h later


Now recall the idea introduced at the beginning of this Topic. It suggested that you drink water to help your cells carry out their functions. When you are very active, you lose moisture from your bodyin your breath and in sweat. Moisture is lost by the body through theskin’s surface and the surface of the lungs. Water is then drawn fromother cells and structures of the body to replace the water lost fromthese surfaces. This happens partly by osmosis and partly as a result ofthe body’s circulatory system. At some point, you need a new supply ofwater to restore the cell water content in your body to its normal level.

Water is important to living things because it dissolves many of thesubstances involved in cell processes. For example, glucose (which cellsuse for energy) dissolves in water to form a glucose solution. Whenwater moves out of a cell, the dissolved substances inside the cellbecome more concentrated. When water moves into a cell, the dissolvedsubstances inside the cell become more diluted.

Water tends to move by osmosis from a diluted solution to a moreconcentrated solution (see Figure 2.15). In other words, water movesfrom a region where it is in high concentration to one where it is inlower concentration. That is why water moves into dehydrated carrotcells. What do you think would happen if you put a fresh carrot stickinto a glass containing a concentrated salt solution? Why might thishappen? See for yourself in the next investigation.

Figure 2.15 Water moves by osmosis from side B to side A inside the beaker. In this simplified diagram, which side represents a carrot stick and which side represents a glass of water?

water particlessolute particles

selectively permeable membrane

A B

A B

Before osmosis

After osmosis

What is the solvent in asalt solution? What is thesolute in a salt solution?For that matter, what is a solution? If youremember these termsfrom your earlier studies,you are ready to doInquiry Investigation 2-F.If you need review, lookup the three terms in theGlossary at the back ofthis book. Write the definitions in yourScience Log.

Can cells break sidewalks? With the help of osmosis, they can!When cells take in water by osmosis, they tend to swell. Theincreasing pressure from the added volume of water may burst

open animal cells. Plant cells, however, can withstand much greater pressure because theyare surrounded by rigid cell walls. This pressure is called osmotic pressure. Have you everseen weeds breaking through a paved sidewalk? They force their way through asphalt byosmotic pressure, generated by water in the cells of the shoot tip.

Looking Ahead

What would happen toa micro-organism ifsalt were added to itswatery environment?How could you testyour prediction? Jotyour ideas in yourplanning file for consideration whenyou do the UnitInvestigation,Responding toChanges.


Safety Precautions

• Handle all glasswarecarefully.

• Never eat or drink anysubstances in thescience laboratory.

Apparatus2 clean beakers (orglass jars) with lids

graduated cylinder

balance

Materials2 uncooked eggs

white vinegar

pen or marker

labels

200 mL distilled water

200 mL salt solution

paper towel

water

Procedure

Prepare two raw eggs a daybefore your experiment bycovering them with vinegarfor 24 h.(a) From your knowledge

of osmosis, predict whatwill happen to the watercontent of an egg placedin distilled water, andone placed in salt solution. Recordyour predictions.

(b) Prepare a table like theone shown here. Giveyour table a title.

Label one jar “distilledwater” and the other jar “salt solution.”

Carefully remove the eggsfrom the vinegar, rinse themwith water, and dry themwith a paper towel. Recordthe appearance of the eggs.

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Egg in distilled water Egg in salt solutionCalculationsOriginal mass of egg

Final mass of egg

Change in mass (+ or –)

Original volume of liquid

Final volume of liquid

Change in volume (+ or –)

Measuring OsmosisJust underneath the shell of an egg is a selectively permeable membrane. In thisinvestigation, you will measure the movement of water by osmosis across thismembrane. What conditions will cause water to move into the egg? What conditions will cause water to move out?

Note: You must start preparing your eggs for this investigation 24 h in advance. You will also need about 24 h to observe the results of osmosis.

QuestionHow can you measure the effects of osmosis?


Measure and record themass of each egg.

Place one egg in each jar.Pour 200 mL of distilledwater into one jar and200 mL of salt solution intothe other. Cover the jars withlids and wait 24 h.

Carefully remove one eggand dry it. Measure andrecord its mass.

Using a graduated cylinder,measure and record the volume of liquid remainingin the jar. (a) Repeat steps 6 and 7 for

the other egg.(b) Wash your hands after

this investigation.

To review how to measure the massof an object and the volume of a liquid, turn to Skill Focus 5.

Analyze1. From your observations, make an inference about the effect

of vinegar on eggshells. Why was this an important first stepin the investigation?

2. What variables are held constant in this investigation? What variable is changed?

3. (a) What happened to the volume of liquid in the jar if themass of the egg increased?

(b) What happened to the volume of liquid in the jar if themass of the egg decreased?

(c) Explain these relationships.

Conclude and Apply4. From your data, make an inference about the effect of

osmosis on an egg placed in (a) distilled water, and (b) saltsolution. In your answer, refer to the movement of waterparticles from a region where water is in high concentrationto one where it is in lower concentration.

Extend Your Knowledge5. Predict what results you might get if you repeated the

experiment with a solution having double the concentrationof salt. Explain your prediction.

6. Draw a flowchart to illustrate the sequence of events in this investigation. Show the movement of particles in the appropriate places.


Fluid Movement in PlantsMost plants need a large supply of water.Plants require water to make sugars in theprocess of photosynthesis. Plants obtainwater from the soil. How does water getfrom the soil into the plants? Roots needthe sugars made in the leaves. How do cellsin the roots of plants obtain these sugars?

Recall from Topic 1 that tissues aregroups of cells that perform similar func-tions. The transport of nutrients is the role of the plant’s tissues. Inside the plant,two types of tissues, called vascular tissues,

connect the roots to the leaves. Phloem tissue transports sugars manufactured in the leaves to the rest of the plant. Xylem tissueconducts water and minerals absorbed by the root cells to every cell in the plant (see Figure 2.16).

Xylem and phloem tissue usually occur together, along the length of the plant stems and roots. Both types of tissue are surrounded andsupported by other tissue that gives the plant strength. This other tissue has large vacuoles for storing food and water.

From Root to LeafIf you examine the structure of a root system, you will see that itsgrowing tips are covered with fine root hairs. These “hairs” are, infact, extensions of single epidermal cells (see Figure 2.17). Epidermalcells form epidermal tissue, which protects the outside of a plant.When the concentration of water in the soil is greater than the concentration of water in the root cells, water enters these root hairs by osmosis.

From the root hairs, water passes from cell to cell by osmosis until itreaches the xylem tissue. The tube-shaped cells making up xylem tissuehave thick walls with holes in their ends (see Figure 2.18). Stacked endto end, they form bundles of hollow vessels similar to drinking straws.Water can flow easily through these vessels. As more water enters theroot hairs, it creates pressure that pushes water up the plant throughthe xylem tissue.

phloem xylem

Figure 2.16 Xylem tissueconducts water from theroots to the rest of theplant. Phloem tissue carriessugars from the leaves tothe rest of the plant.

The phloem of a tree lies close to the outer surface of the trunk, just below the bark.Because of this, sugar tappers can easily draw sugar solution from the trunks of mapletrees. This is done by boring a small hole through the bark and pushing small tubes into thephloem tissue. The best time to tap maple trees is early in the spring, when large amountsof sap are flowing to provide energy for new growth.


Water is transported by xylem tissue intothe stems and the leaves. Leaves are theplant’s food-producing organs. Recallthat photosynthesis manufactures sugarsfrom water, carbon dioxide, and sun-light. Most photosynthesis takes placein a layer of cells in the leaf that arefilled with chloroplasts. These cellsare called palisade cells. Why aremany leaves typically flat and thin?This shape provides a large surfacearea to absorb sunlight. This shapealso makes it easy for gases to diffuseinto the leaf cells (see Figure 2.19).

Notice the tiny openings on theunderside of the leaf. These open-ings are called stomata (singular:stoma). They allow air to enter theleaf, supplying the oxygen the cells needfor respiration and the carbon dioxide theyneed for photosynthesis. Spaces between leafcells allow the air to flow around each cell.Surrounding each stoma are guard cells, whichcan expand to close off the stoma.

TranspirationWhy do the stomata in a leaf open and close? Toanswer this question, recall that water first entersa plant through its root system. Then it movesinto its shoot system. What happens next? Thewater does not continually circulate like theblood in our bodies. It does not go back into theroot system. Instead, it exits the plant —through the open stomata in the leaves.

This loss of water from a plant through evaporation is called transpiration. The loss ofwater is not a problem as long as it is replacedby more water that enters the plant through the roots. In periods of drought and in deserts,however, water loss from a plant can be a serious problem.

epidermal cells

soil particles

water and minerals

root hair

Figure 2.17 Water and dissolved minerals enter the plantby osmosis through the root hairs.

Figure 2.18 Xylem cellshave thick walls forstrength. Their open endsallow water to passthrough freely.


Figure 2.19 The structure of a typical leaf

waxy layer

palisadecell

water leaves

stomata

guardcells

sunlight

epidermis

epidermis

vein (includes xylem and phloem tissue)

carbon dioxideenters

Find OutTranspiration and LeavesWhat is the relationship between leaves, trans-piration, and the movement of water through aplant? You can find out by doing this activity.

Materials

2 leafy stalks of celery

beaker (or jar) of water

red food colouring

single-edged razor blade or sharp knife

cutting board or other cutting surface

Procedure

1. Take two leafy stalks of celery of about thesame length.

2. Remove all the leaves from one stalk.

3. Place both stalks in a beaker or jar ofwater to which red food colouring hasbeen added, as shown in the diagram.

4. Leave the jar in a sunny spot or under abright light for at least 3 h.

5. Place the stalks on a cutting board.Beginning near the bottom end of thestalks, cut across the stems at short intervals to determine how far the coloured water has risen up each stalk.

Never cut an object held in yourhand. Place the object on a cutting surfaceand cut with the blade moving away fromyou. Cut the celery stalk with your teacherpresent.


1. Based on your observations, what inference can you make about the effect of leaves on the rate of transpiration?


CAUTION

celery stalkwith leaves

celery stalkwithout leaves

food colouringin water

beaker


Pulling and PushingIf all the tissues of a plant were to magically disappear, leaving only thewater in them behind, you would see a ghostly outline of the plant in aweblike network of water. There is no break in this water system. Finecolumns of water connect every cell, from the leaves to the roots. Thenetwork extends even beyond the root hairs — it connects root hairs tochannels of water in the soil.

According to the particle model, individual water particles are heldtogether by bonds of attraction, which make the plant’s water networkbehave as a single unit. Water drawn into the root hairs by osmosispushes slender water columns up the plant. At the same time, water lostfrom the leaves by transpiration pulls water up the xylem tissues all theway from the roots. Both these actions — pushing and pulling — arenecessary to raise the water up to the top of very tall trees. In this way,trees can transport water without having a pumping organ similar tothe human heart.

1. What process causes water to enter or leave a cell?

2. How are osmosis and diffusion alike? How are they different?

3. If your teacher opens a bottle of ammonia at the front of the classroom,you will smell ammonia at the back of the room a short while later.Explain what has occurred.

4. Which tissues conduct water in plants?

5. Which tissues conduct sugars in plants?

6. What is the function of guard cells?

7. Apply Why do grocery stores spray their fresh vegetables with water?

8. Design Your Own Is it better to water plants in the evening or duringthe day? Make a hypothesis that answers this question, and then design anexperiment to test it. Remember to include a control in your experiment.

9. Design Your Own Choose one of the following:(a) Design an experiment to test the effectiveness of different substances

in preventing flowers from wilting.(b) Formulate your own question about some aspect of cell functioning,

and design your own experiment to explore possible answers.

T O P I C 4 Review


T O P I C 5 Cell Specialization andOrganizationImagine an orchestra made up of only a hundred trumpet players or a hundred violins. Such an orchestra would be very limited. To playevery kind of music, an orchestra needs a variety of musical instru-ments, each with its own special sound. In an orchestra, the sameinstruments and those that are similar are grouped together so they can work together more easily to make their particular, unique sound.In the same way, a multicellular organism has different kinds of cells,which are organized in ways that help them to do their jobs.

Specialized CellsAlthough multicellular organisms grow from single cells that repeatedlydivide, their cells are not all the same. Like the instruments in anorchestra, different cells have different appearances and perform different jobs. They are said to be specialized for particular tasks. Forexample, your muscle cells are shaped to move parts of your body, andyour skin cells are built to protect your body from the drying rays ofthe Sun. Humans have about a hundred different types of cells, eachwith its own particular structure and functions.

Figure 2.20 Different cells have different shapes and functions.

Look at the examples of plant and animal cells in Figure 2.20. How dotheir shapes relate to their functions? Nerve cells have long, branchedfibres running from the main part of the cell, shaped to carry nerve signals from one part of the body to another. Red blood cells, whichcarry oxygen in the bloodstream, have a thin, disklike shape. This givesthem a large surface area to pick up large amounts of oxygen. Thewater-conducting cells of a plant are tubelike, with thick walls and a network of holes that lets water pass easily through them. Onion skincells are flat and brick-shaped, so they can fit closely together to form a continuous protective layer.

A nerve fibre in theneck of a giraffe can beup to 1 m in length.However, the main partof the cell from whichit comes is about thesame size as a humannerve cell.

nerve cell

water-conductingplant cell

onion skin cell

red blood cell

Cell Specialization and Organization • MHR 139

Most household dust ismade up of dead humanskin cells. You and everyone around you arecontinually sheddingparts of the thin outerlayer of skin. Your entireouter layer of skin iscompletely replaced bythe growth of new cellsapproximately every28 days.

Now look at the photographs of different cells below and thinkabout the structure of each and what function it might perform. Canyou match the cells that come from the following part of your body —blood in your heart, nerve in your toe, muscle in your arm, bone inyour leg, and skin on your head?

The Advantages of Being MulticellularImagine you are a microscopic, unicellular organism. Your whole bodyis one cell. This one cell must carry out all the functions needed tokeep you alive. It must be able to move, obtain food, reproduce, andrespond to the environment. There are many living organisms thatconsist of only one cell. What disadvantages do you think they have,compared with multicellular organisms?

You have already learned one disadvantage. Unicellular organismscannot grow very large. Also, because they must take in all the materi-als they need through their cell membranes, most unicellular organismscan only live in watery, food-rich surroundings.

A B C

D E


Cell OrganizationMulticellular organisms have several advantages compared to unicellular living things. They can live in a wide variety of environ-ments. They are able to grow very large — as large as a whale or aDouglas fir. Multicellular animals can obtain their energy from a widevariety of foods. Their bodies are more complex. By specializing in particular functions, each cell in a multicellular organism can workmuch more efficiently than the cell of a unicellular organism.

In multicellular organisms, specialized cells of a similar kind workclosely together, and are usually found grouped closely together in the body. Groups of specialized cells, in turn, work in harmony withother groups.

Figure 2.21 The body of this whale contains trillions of cells that are grouped into tissues,organs, and systems.

Many animals and plants are made of trillions of cells. To learn howthese cells are organized, compare the organization of cells with theway students are organized in a school district. First, students in thesame grade are grouped together in classes. Then, different classes ofstudents together make up a school. Finally, a number of schools areorganized into a single school district.

Similarly, as you saw at the beginning of Topic 1 (page 100), cellswith the same structure and function are grouped into tissues. Groupsof different tissues form organs. Organs work together in systems.Systems work together to form an organism. This arrangement of cells,tissues, organs, and systems forms several different levels of organiza-tion in living things. Each level can be studied on its own, as you havedone with cells. Or they can be studied in relation to the levels aboveor below it, as you have done with plant cells and tissues.


TissuesTissues are groups of similar cells. Onion skin is a tissue made of sheetsof similar, thin, tightly packed cells. These specialized skin cells form alayer that covers and protects the onion. Figures 2.22 and 2.23 show the main types of tissues found in animals and plants. These tissues are classified according to the functions they perform.

Muscle tissuemoves parts of the body.

Nerve tissue carries signals between the brain and other body parts to co-ordinate activities.

Connective tissue(bone) connects and supports different parts of the body. May be solid, like this bone tissue, or fluid like blood. Blood transports substances throughout the body. Other connective tissue forms loose, fibrous sheets between body parts.

Epithelial tissue(skin) protects the outside of the body and also covers internal structures, such as the intestines.

Figure 2.22 Main types of tissues found in animals Figure 2.23 Main types of tissues found in plants

Xylem tissuevessels transport water absorbed by the roots, throughout the plant.

Phloem tissue vessels transport the glucose — sugar — made in the leaves byphotosynthesis to other parts of the plant.

Epidermal tissue (skin)protects the outsideof the plant.


OrgansSuppose you feel hungry, see ajuicy apple, and eat it. Thissimple action would not bepossible without the next levelof organization in the body —the organs. Organs are distinctstructures in the body thatperform particular functions.You used your eyes (to sensethe apple), your brain (to planand co-ordinate your actions),and your mouth and stomach(to start digesting the apple).Each organ is made of severaltissues working together. For

example, your stomach is made of four main types of tissues, as shownin Figure 2.24. Other examples of organs in your body are the lungs,the heart, and the kidneys. Plants have organs, as well. Plant organsinclude roots, stems, and leaves.

Figure 2.24 The stomachis an organ made ofdifferent tissues.

muscle tissue(moves to mix

stomachcontents)

epithelial tissue(lines stomach)

connective tissue(holds shape)

nerve tissue(co-ordinates

activities)

Find OutLooking at Animal TissuesThe photographs below show tissues observedunder a compound light microscope similar tothe one you have used.

Procedure

1. With your group, look closely at the tissuesshown in A, B, and C. The tissues arebone tissue, nerve tissue, and skeletalmuscle (the kind of muscle you use, forexample, to bend your arm).

2. Based on whatyou have read about these tissues, try to

identify each type. Record your decision andreasons for your decision for each tissue.


1. Which tissue did you find easiest to identify and why?

2. List three different careers in which a person might need to examine tissues.Suggest at least one way a person could use information obtained by observing tissues.




A B C


Teamwork!

Think About ItWhy do you need a liver? A heart? A pair oflungs? What do these and other organs do? What are their main parts? Are they part of a system? Your class will divide into small groups toinvestigate these questions and each group willpresent its findings to the class. How you com-plete this task is up to your imagination and yourresearch skills!

What to DoAs a class, brainstorm a list of organs found inthe human body. Divide into groups andassign one organ to each group.

Decide how the class will evaluate eachgroup’s presentation. As a minimum, eachgroup’s presentation must answer these threequestions:• What is the organ’s function?• What is the organ’s structure?• To which system does the organ belong?

Use your library, the Internet, and any otherresources to research the structure and func-tion of your group’s organ. Here are somemore ideas to start you thinking:

• What happens if the organ does not workproperly?

• Can the organ be transplanted? Can it bereplaced by an artificial organ?

• Which other animals have this organ? Arethere some interesting differences or simi-larities compared with the human organ?

Decide how your group will co-ordinate and present the results of its research to theclass. Your group may choose to do one of the following: • present a scientific lecture with charts and

graphs• write a play and act the roles of tissues, cells,

and organs• devise a quiz modelled on games such as

“20 Questions” or “Jeopardy”• invent a board game• construct a three-dimensional model.

2-G2-G

www.school.mcgrawhill.ca/resources/For information about organs in the human body

and diseases affecting them, visit the above web site. Goto Science Resources, then to SCIENCEFOCUS 8 to find

out where to go next. Search for facts or diagramsthat you might use in this investigation.

S K I L L C H E C K





AnalyzeUse the criteria decided in advance (see step 2)to evaluate each group’s presentation.


SystemsAs you have seen, organs work togeth-er just as cells and tissues do. Organsform systems to perform activities thathelp plants and animals function as awhole. Because of differences in howplants and animals survive, plants havefewer systems than animals have.Plants have only two main systems: aroot system below ground and a shootsystem (the stems and leaves) aboveground, as shown in Figure 2.25. The

functions of the root system are to obtain water and minerals from thesoil and to anchor the plant in the ground. The function of the shootsystem is to make food for the plant. At certain times, flowering plantsproduce a third system for reproduction. The reproductive system caninclude flowers, fruits, and seeds.

1. Why do cells in your body need to be specialized?

2. Why do nerve cells have long fibres, whereas red blood cells are thin anddisklike?

3. Why do unicellular organisms live mainly in a watery environment?

4. Choose the correct answer and write each complete sentence in yournotebook.(a) A tissue is made from groups of (i) organs, (ii) cells, (iii) organelles.(b) Muscle is an example of (i) a system, (ii) an organ, (iii) a tissue.(c) The heart is an example of (i) an organ, (ii) a system, (iii) epithelial

tissue.(d) One example of connective tissue is (i) nerve tissue, (ii) bone tissue,

(iii) epithelial tissue.(e) An example of a system in plants is (i) seeds, (ii) the shoot system,

(iii) xylem.(f) The type of tissue that protects the outside of a plant is called

(i) epithelial tissue, (ii) epidermal tissue, (iii) connective tissue.

5. Apply Most people think of the skin as just a body covering. How doyou think skin cells are important to other body cells?

T O P I C 5 Review

stem

leavesshoot system(stems and leaves) andreproductive system (flowers,fruit, and seeds)

flower

fruit withseeds inside

root system

root

Figure 2.25 The purposeof each system is toprovide the organism withwhat it needs to stay alive.



2. Draw a flowchart illustrating the followingterms in the correct order:organs, cells, tissues, organism, systems. (5)

Understanding Key Concepts3. Compare cell membranes with the screen

doors used on houses in summer. Explain whyneither can be completely impermeable orpermeable. (4)

4. How are osmosis and diffusion different? (4)

5. If a cell is placed in a concentrated solution ofglucose, would you expect water to move intoor out of the cell? Explain. (4)

6. Explain why cells need (a) water, and (b) food. (4)

7. Why might a plant with a huge stem system and a tiny root system have difficultysurviving? (4)

8. Why are cells specialized in multicellular organisms? (5)

9. Name the main types of specialized cells in animals. (5)

10. Explain how the structure of a specialized cell is related to its function in the body of amulticellular organism. (5)

11. List some advantages that multicellular organ-isms have over some unicellular organisms. (5)

12. Name the five levels of organization in a multicellular organism and give an example of each. (5)

13. Give two examples of systems in plants andexplain their functions. (5)

14. Study the two photographs of red blood cells.One cell was part of a group of cells placed indistilled water, while the other was placed in astrong salt solution. Make an inference aboutwhich one was in which solution, giving yourreasons for your inference. (4)


Key Termsselectively permeablepermeableimpermeablediffusion

osmosisvascular tissuesphloem tissuexylem tissue

root hairstranspirationspecializedtissues

organssystemslevels of organization

• A cell membrane is

• Water enters or leaves cells by

• Oxygen enters or leaves cells by

• Water evaporates from a plant by

• osmosis (4)

• diffusion (4)

• transpiration (4)

• selectively permeable (4)

• permeable (4)

BA

Reviewing Key Terms1. In your notebook, complete each sentence from column A with the correct

ending from column B.

A B


T O P I C 6 Body Systems in HumansAs you learned, every cell in the body needs a steady supplyof food and oxygen to give itenergy. Three different organsystems must work together tomake this possible. Do you knowwhat they are?

The Digestive SystemFood first enters the bodythrough the mouth, then passesto the stomach and the intestine.It is broken down along the wayinto small, soluble particles thatcan be used by cells. Unusedfood is expelled from the bodyas waste. The organs involvedin these processes form thedigestive system, as shown inFigure 2.26.

The Respiratory SystemBreathing in (inhalation) fills our lungs with oxygen-containing air. Breathing out (exhalation)rids our bodies of waste carbon dioxide. Theorgans involved in this gas exchange form therespiratory system, as shown in Figure 2.27.

The Circulatory SystemThe digestive system puts food into the intestineand the respiratory system puts oxygen into thelungs. How do particles of food and oxygen eventually get from these systems to cells in thetoes, the brain, and other parts of the body? Athird system transports particles of food and oxygen. The circulatory system consists of theheart, blood, and blood vessels (see Figure 2.28).This system circulates blood around the body,delivering food particles, dissolved gases, and other materials to every cell and carrying awaycell wastes.

larynx

trachea

bronchus

lungs

bronchioles

diaphragm

alveolus

Figure 2.27 This system moves air in and out of thebody. This in-and-out movement of air supplies oxygenfor cells and removes waste carbon dioxide.

Figure 2.26 This organ system breaks down foodby digestion.

There are 11 differentsystems in the humanbody. Each system has amajor function. The sys-tems are co-ordinatedinto the total livingorganism, and all thesystems depend on oneanother.

Body Systems in Humans • MHR 147

Heart and Major Arteries and Veins of the Body

veins from the head

veins from the arm

vein from kidney

veins from legs

veins taking bloodto heart

arteries to the head

arteries to the arm

arteries to legs

artery to kidney

right atrium receivesblood from body

left atrium receivesblood from lungs

right ventricle pumps blood to lungs

left ventricle pumps blood out to the rest of the body

The human heart has four compartments: the right atrium, the right ventricle, the left atrium, and the left ventricle.

aorta

pulmonaryartery

valve

valvevalve

left atriumright atrium

left ventricleright ventricle

large vein from upper regions of body

large vein from lower regions of body

veins from lung

valve

arteries

Figure 2.28 The circulatory system’s function is to carrymaterials to and from all the cells in the body.

Find OutChanging Your Pulse RateYour pulse is produced by blood surgingthrough your arteries each time your heart“beats.” It is one guide as to how well your cir-culatory system is working. What factors affectthe rate at which your heart pumps blood?Measure your pulse rate to find out.

Procedure

1. Locate one of your radial arteries, on theinside of your wrist in line with your thumb(see the photograph).

2. Using a watch or timer, count the numberof pulses you feel in 15 s while you are sit-ting comfortably at rest. Multiply the num-ber by 4 to obtain your heart rate perminute. Record your results.

3. Stand up and do five deep knee bends asshown in the photograph. Immediately measure and record your pulse rate.

Do not do this activity if you haveany health problems that may put you at risk.

4. Rest for 1 min and again measure andrecord your pulse rate.


From your results, what is the relationshipbetween exercise and pulse rate? Suggest anexplanation for this relationship.


CAUTION


How the Respiratory and Circulatory Systems ConnectTo connect the cells throughout your body with the air, the respiratorysystem and the circulatory system work together.

The respiratory system exchanges oxygen and carbon dioxide, whilethe circulatory system transports those gases throughout the body. Thegases pass from one system to the other where the two systems comeinto closest contact — among the tissues of the lungs.

Look at Figure 2.27 on page 146. After air enters the nose, it passesto the lungs through a series of smaller and smaller tubes. The trachea(windpipe) is about 20 mm in diameter. It divides into a right and a leftbronchus, each about 12 mm across. Each bronchus tube branches intothousands of small, narrow bronchioles, with diameters of 0.5 mm.Finally, the bronchioles divide and end in millions of tiny air sacs calledalveoli (singular alveolus), only 0.2 mm in diameter.

The circulatory system also involves a series of tubes — the bloodvessels. Blood vessels branch and divide into smaller and smaller channels. The three main types of blood vessels are shown in Figure 2.29. The smallest blood vessels are the capillaries.

Figure 2.29 Cross sections of human blood vessels

Diffusion causes oxygen to pass from the alveoli into the capillaries.The oxygen first dissolves in a thin film of moisture covering the wallsof the alveoli. Then it diffuses from the alveoli through the thin capil-lary walls into the bloodstream.

Arteries have thick,muscular walls forcarrying blood underpressure.

Veins have thinner walls than arteries. Valves inside veins prevent blood fromflowing backward.

Capillaries are hair-thin vessels. Their walls aremade of epithelial tissueonly one cell layer thick.

epithelialtissue

muscle

artery vein capillary (enlarged diagram)

outercase

innerlining


A capillary may be sonarrow that only one redblood cell can passthrough it at a time.


Now look closely at Figures2.30A and B on page 149.Each alveolus is surroundedby a web of capillaries. It ishere that gases areexchanged. Oxygen and carbon dioxide pass backand forth between the air in the alveoli (part of therespiratory system) and the blood in the capillaries(part of the circulatory system).

How the Circulatoryand DigestiveSystems ConnectYou have discovered how your blood-stream obtains oxygen from your lungs.Your bloodstream also carries food particles. The transfer of food from thedigestive system to the circulatory systemtakes place at the inner lining of thesmall intestine, as shown in Figure 2.31.Covering the surface of this lining aremillions of tiny, fingerlike projectionscalled villi (singular: villus). Each villuscontains a network of capillaries.Dissolved food particles pass from theintestine into the capillaries by a processcalled absorption. The food particles are now small enough to enter yourbody’s cells to supply them with the food they need. The arteries of your circulatory system provide the transportation network.

Like alveoli, villi have thin wallsthrough which particles can pass into the circulatory system. Both alveoli and villi consist of tiny projections, and both occur in huge numbers. Thisarrangement greatly increases the surfacearea that is in contact with capillarieswithout taking up a large amount ofspace in the body.

blood vessel

villi

Figure 2.31 The villi in the small intestine. These structures increasethe surface area of the small intestine for more efficient absorption of nutrients.

Figure 2.30B An enlarged alveolus. Thereare about 300 million alveoli in the humanlungs.

Figure 2.30A Gases move back and forthbetween the alveoli and the surroundingblood vessels.

alveoli

arterybronchiole

capillaries

vein

alveolar sac

alveolus

air red bloodcells

capillary

CO2

CO2

CO2CO2

CO2

O2

O2

O2

O2

O2

CO2 = carbondioxide

O2 = oxygen


Many seals, with lungs nobigger than a human adult’s,can easily stay underwater

without breathing for 20 min or more. Even more curious,they breathe out before they dive. The explanation for thispuzzle lies in how the seal’s blood and circulatory systemfunction. All the oxygen a seal needs while underwater isstored in its blood and muscle tissue, rather than in its lungs.To be able to store this large amount of oxygen, a seal hasabout one-and-a-half times to twice as much blood in itsbody as other mammals of similar size.

As soon as a seal dives underwater, a series of changes takesplace in its body. Its heartbeat slows at once, from about 100beats per minute to about 10 beats per minute. Blood flow to

some parts of its body,such as the kidneys andthe muscles, slows orstops. The seal is alsoable to tolerate a highlevel of carbon dioxide inits blood, as this gasbuilds up during the dive.

When the seal returns tothe surface, it can breathein and out very rapidly, almost completely emptying its lungsof waste gas. With each breath, a seal can exchange 90 percentof the air in its lungs. By comparison, with each breath, humansexchange only about 20 percent of the air in their lungs.

Find OutMake a Model of the LungsIf you look at lung tissue under a microscope,you will see that it has no muscle cells. Sowhat makes your lungs expand and contract?Make a model of your lungs and chest cavityto find out.

Materials

large plastic pop bottle 2 plastic straws

2 small balloons 2 elastic bands

modelling clay

Procedure

1. Inflate the balloons to stretch them, thenlet out the air. Insert a straw into the neckof each balloon and fasten the balloon andstraw tightly together, using elastic bands(see Diagram A).

2. Insert the straws into the bottle so the balloons are hanging inside the bottle, andthe other ends of the straws are stickingabove the neck, as in Diagram B.

3. Completely seal the neck of the bottlearound the straws with modelling clay, as shown in Diagram C.

4. Squeeze and release the sides of the bottle and watch what happens to the balloons.


1. What happened to the balloons when thebottle was squeezed? What happenedwhen the bottle was released?

2. Write an explanation for your observations.Try to use the term “air pressure.”

3. In what way is the squeezing and releasingof the bottle similar to inhaling and exhaling?


A

B

C


Find OutEmployment — Excretion!Imagine you are a body in search of kidneys. You must write a job description to get theright organs for the job. What exactly must kidneys do? What qualifications (structure) dothey need? Will they be expected to work inco-operation with other organs? Present yourjob description in class.

Procedure

1. Do some research on kidneys and the excretory system to answer the questionsabove.

2. Present your findings in the form of a job advertisementwith the heading: “Wanted: HighlyQualified Kidneys.” The ad should givedetails of kidney structure and functions,and it should include a labelled sketch.


1. What waste materials do kidneys removefrom the body, where do these wastescome from, and why must they be removed?

2. Which other system is most closely connected with the excretory system?


The Excretory SystemGetting food and oxygen to your cells is only one half the equationfor good health. Your body must also get rid of wastes. Filteringwaste materials from the blood is the main function of another system — the excretory system. The key organs in this system areyour two kidneys. You can research this system for yourself in theFind Out Activity below.

Sensory Awareness SystemsFeeling cold? Why not put on a sweater? Feeling hungry? It’s time to eat. In these and other ways, you respond to changing con-ditions and make adjustments. Your body systems also make constantadjustments to maintain a stable internal environment for your cells.

For example, nearly 90 percent of your body heat is lost through theskin. Most of the rest of your body heat is lost through your lungs.When you get cold, you may shiver. Your quivering muscles generateheat. You may also get “gooseflesh” — small bumps on your skin. Thebumps are produced by the contraction of small muscles in the skinthat make your hairs stand on end. In animals with a thick coat of hair,and in our hairier prehistoric ancestors, fluffing up the body hair helpsreduce heat loss by improving insulation.

When you are hot, your body tries to cool you down. Do you getflushed and red after hard exercise? This happens because tiny bloodvessels in your skin expand. This increases blood flow near the bodysurface where heat can be lost to the outside. Sweating helps cool yourbody as the moisture evaporates from your skin surface.


To keep your body temperature stable, your nerves, muscles, andblood all function together. Your nervous system monitors conditionsoutside the body through temperature receptors in your skin.Information from the temperature receptors goes to the heat-regulating centre of your brain (the hypothalamus). Responding to thisinformation, the brain sends nerve signals to your muscles, skin, andblood vessels. Working together, your muscles, skin, and blood vesselsadjust your blood flow and muscle activity. In response, your bodyincreases its heat production or reduces its heat loss.

Your body’s responses to stimuli are co-ordinated by the nervoussystem (the brain, spinal cord, and nerves) and the endocrine system (glands that produce chemical messengers called hormones). In the body, a number of factors can affect the smooth working of thebody systems (listed in Table 2.1 on page 153).

Find OutA Simple ReflexThe knee-jerk reaction is a simple example of a feedback system controlled by the nervoussystem in the body. A sharp tap (stimulus) atthe knee causes a signal to be sent to thespinal cord. A return signal (the feedback)causes the leg to react to the stimulus (see the diagram below). You can observe this feedback system for yourself.

Materials

rubber reflex hammer

Procedure

1. Your teacher will ask for two volunteers tocome to the front of the classroom. One student sits on the edge of a bench ortable so his or her legs hang freely and donot touch the floor.

2. The second student locates the first stu-dent’s kneecap and feels the position of thetendon at its lower edge. With the rubberhammer, or the edge of a hand, the secondstudent (guided by the teacher) quickly andfirmly taps the tendon. Note the automaticresponse of the lower leg.

3. The students will change roles and repeatsteps 1 and 2.


1. Which muscles contract to lift the leg?

2. Draw a flowchart showing the sequence of events from tapping the tendon to theresponse of the leg.


spinal cord

nerve impulse from patella

nerve impulse to leg muscle

femur (thigh bone)

tibia (leg bone)

patella (knee cap)

mallet


1. Why does the body need oxygen?

2. Describe how carbon dioxide from a cell in your hand leaves your body.

3. The lungs can expand and contract because they have muscular walls. Isthis statement true or false? Explain.

4. What structures help increase the absorption of food in the small intes-tine? How do they do this?

5. How might your muscular system help you stay warm?

6. How might your circulatory system help you stay cool?

T O P I C 6 Review

In 1921, Canadian researchers FrederickBanting and Charles Best, working at theUniversity of Toronto, discovered the hor-mone insulin. This hormone, produced bycells in the pancreas, sends a message toother cells in the body when there is a lot of glucose in the blood. The cells respond by processing the glucose, which lowers theblood’s glucose level. Hormone productionis constantly adjusted by the pancreas asglucose levels rise and fall. (The amount ofglucose in a person’s blood depends on their eating habits and amount of physicalactivity.)

Some people’s bodies are unable to controlthe glucose levels in their blood. This leadsto the disorder called diabetes. Before thediscovery of insulin, diabetes was fatal.Today, people with diabetes are able to livefull lives by controlling their diets and byinjecting insulin, if their bodies cannot makeit for themselves.

AcrossCanada

Drug addiction or dependence is an exam-ple of how our bodieswork to provide a stableinternal environment.When the body is firstexposed to a drug(whether caffeine, nico-tine, opium, or anotherchemical), the cellsrespond so as to main-tain their normal functionin the presence of thenew chemical. After atime, the cells become so tolerant that the drugloses its effect. The person may then need totake larger quantities ofthe drug to produce thedesired effect. If the sub-stance is withdrawn, thecell response is disturbedfor a time — sometimesseverely — until a newreadjustment is made.

Diet, exercise, drugs, injury, and disease can affect body systems anddisrupt how they function.

Table 2.1 Major Body Systems

FunctionsSystemDigestive

Respiratory

Circulatory

Nervous

Excretory

Breaks down food, absorbs food particles, and eliminates wastes.

Exchanges oxygen and carbon dioxide.

Circulates blood. Transports food particles, dissolved gases, and other materials.

Controls and co-ordinates body activities. Senses internal and external changes.

Regulates blood composition and excretes waste fluids.

Ask anExpertTurn to page 164 tofind out what anotherresearcher is doingtoday to find a cure fordiabetes.


T O P I C 7 Body Systems and Your Health

During the fast-paced excitement of a hockeygame, both players and spectators experiencerapid breathing and heart rates. This happensbecause our muscles demand more oxygen andnutrients as our activity level rises. Our heartresponds by pounding more than twice as fast aswhen we are asleep. Throughout our lives, duringactive as well as quiet moments, the heart workscontinuously to deliver nutrients and removewastes from every cell of our bodies.

If you press your fingers to your chest a few centimetres left of thecentre, you may be able to feel the thumping of your heart. Thatrhythmic pulse is evidence of a pump at work, pushing your blood in acontinuous flow through all the vessels of your body (see Figure 2.32).

Blood — The Body’s Transportation SystemIn unicellular organisms, materials are directly exchanged between

the cell and its external environment, as shown in Figure 2.33. In multi-cellular organisms, most cells are not in direct contact with the externalenvironment. Substances must be brought to cells and taken away fromthem by the circulatory system. The blood vessels of the circulatory system form a complex network linking the outside environment with

the internal environment of the body.In humans, substances are transported around the

body in the blood. About 8 percent of an adult’s bodyweight is blood. What exactly is blood made of? Themain components of this fluid and their functions are listed in Table 2.2. Plasma and red blood cells make up 99 percent of the volume of blood. Plasma is the liquidportion of the blood. It transports most of the carbondioxide produced by the body. The red blood cells arespecialized to carry oxygen. They contain an iron-richchemical called hemoglobin, which attracts oxygen. This allows the blood to carry much more oxygen than it otherwise could.

Figure 2.32 The heart is a pumping organ. Youcan feel it contracting and relaxing as it pushesblood through your arteries.

Body Systems and Your Health • MHR 155

Figure 2.33 Paramecium exchanging materials with its external environment.

Table 2.2 Blood Components and Their Functions

Just as highways bring materials from outside your neighbourhood, thecirculatory system continuously brings oxygen and nutrients from theoutside environment into your body. In order to do this, it works closelywith two other systems, the respiratory and the digestive systems.

If one of these systems is not functioning properly, the whole network is disrupted and the entire body is affected. Leading causes of hospitalization in Canada are disorders of the circulatory system (15 percent), digestive system (11 percent), and the respiratory system (10 percent).

A Healthy Circulatory SystemThe pumping action of the heart circulates the blood throughout thebody, supplying oxygen and food that cells need for their activities. The circulating blood also carries wastes produced by the cells to otherorgan systems that break them down or excrete them from the body.

Disorders of the circulatory system are the leading cause of death in North America. One of the most common is high blood pressure(hypertension). High blood pressure can affect the circulation of theblood and can lead to heart attacks (damage to heart muscle) andstrokes (brain damage). High blood pressure is sometimes known as the “silent killer” because people with hypertension may not feel ill.

Percentage of blood (by volume)

Main functionComponent

plasma

red blood cellswhite blood cells

platelets

55%

44%less than 1%

less than 1%

carries nutrients, waste products, hormones, and blood cellscarry oxygendefend body against infection and diseasecause blood to clot (thicken) at site of wounds to prevent blood loss

wastes

nutrients

(internalenvironment)

(externalenvironment)

oxygenparamecium

carbondioxide

inside cell

water

Iron (found in red bloodcells) is obtained fromcertain foods, such asliver, egg yolks, beans,nuts, dried fruits, andleafy green vegetables. A shortage of iron in the body may result inanemia. This is a condi-tion in which the blood’sability to carry oxygen is greatly reduced.Symptoms of anemiainclude dizziness, faint-ing, and shortness ofbreath. The problem can be remedied by animproved diet that is rich in iron.


Cells need to divide so your body can grow and repair itself. What happens if cells begin to divide and spread in an uncontrolled way? This is what happens in the bodies of people with cancer. As abnormal cancer cells continue to multiply, they spread to other parts of the body and damage them.

There are some treatments that can slow or stop the spread of cancer by destroying the cancerous cells and leaving normal cells intact. This can be done by chemicals(chemotherapy) or radiation (high-energy particles). These

treatments are most successful if the cancer is diagnosed inthe early stages, before the abnormal cells have spreadwidely through the body.

New techniques may give better methods of curing cancer inthe future. One method is gene therapy — the changing ofgenes that cause cells to divide and produce cancer.Alternative therapies focus on ways to boost the body’s ownnatural immune system. For example, people may be able touse vaccines or drugs that stimulate their bodies to destroycancer cells, making them immune to cancer.

Blood PressureDoctors measure blood pressure as a simple firststep to assess the health of the circulatory system.The device used to measure blood pressure is calleda sphygmomanometer (see Figure 2.34). It consistsof an inflatable cuff that is wrapped around the arm.Air is pumped into the cuff, squeezing it against theartery in the arm and restricting the blood flow. Airis then slowly let out of the cuff to the point wherethe blood pressure matches the cuff pressure, lettingblood force its way back through the artery. A doc-tor can listen for the sound of the blood using astethoscope (see Figure 2.35).

Blood pressure indicates several things about thehealth of the circulatory system:• The volume of blood: If a person has lost a lot of

blood through injury, the blood pressure will be low.

• Heart rate: A fast-beating heart pushes bloodrapidly through the arteries, building up bloodpressure.

• Artery size: Large, open arteries conduct larger volumes of blood, producing low blood pressure.Small, narrow, or partly clogged arteries producehigh blood pressure.

• Artery elasticity: Flexible arteries can easily expand,letting more blood through. Loss of elasticityresults in “hardening” of the arteries, producinghigher blood pressure.

• Blood viscosity: Viscosity refers to the thickness ofthe blood. Thick fluids flow less easily than thin,watery fluids. Blood viscosity is a measure of thebalance between red blood cells and plasma.

no pulsesounds

pump

stethoscope

brachialartery

sphygmomanometer

160

Figure 2.35 A doctor uses both a sphygmomanometerand a stethoscope to measure blood pressure.

Figure 2.34 Measuring blood pressure


Disorders of the Circulatory SystemCertain conditions place people at greater risk of disorders of the circu-latory system. Some of these are smoking, a high level of cholesterol inthe blood, high blood pressure, and lack of regular exercise.

For example, cigarette smoke is a double threat to the circulatorysystem. Nicotine in cigarette smoke causes blood vessels to constrict,increasing the heart rate and raising blood pressure. Also, carbonmonoxide in the smoke competes with oxygen in the lungs. Thisreduces the blood’s ability to carry oxygen to the cells.

A poor diet can also lead to disorders of the circulatory system. Forexample, a high-salt diet can raise the blood pressure, putting greaterstrain on the heart. The heart gradually increases in size and becomesless efficient. High-fat diets can cause fats such as cholesterol to buildup inside arteries. As arteries narrow and become blocked, tiny tears in their walls cause blood clots that can travel to the brain causing astroke. As well, blood flow through the arteries can become very limitedor stop, causing a heart attack (see Figures 2.36A and 36B).

Risks of disorders to the circulatory system can be reduced or avoid-ed by choosing healthy lifestyle habits: not smoking, eating a properdiet, and getting regular exercise.

Research conducted by scientists has shown a link between heart disease and high levels of cholesterol in the blood. Cholesterol is a chemical that can cause the buildup of fattydeposits on artery walls. Some people assume that any cholesterol in the body is unhealthy.In fact, the liver produces this chemical, which is involved in maintaining nerve cells andhelping the body use certain hormones. Normal levels of cholesterol are necessary for goodhealth; high levels can contribute to poor health.

Figure 2.36A This cross section of a healthy artery shows aclear, wide-open pathway through which blood flows easily.

Figure 2.36B Here the blood-flow path has been narrowed bya buildup of fatty deposits and blood flow is slowed.

A Healthy Digestive SystemThat old saying, “What you put into something is what you get out of it” also applies to your body. The foods we eat contain differentcombinations of substances. Some of these substances provide energyand materials for cell development, growth, and repair, and are oftencalled nutrients. Other substances in foods can cause poor health andpromote disease when consumed in large quantities over long periodsof time.

Nutrients in FoodStarch and sugars are carbohydrates and provide the body with its mainsource of energy. Starch is a complex carbohydrate found in fleshyfruits, cereal grains, beans, and peas. It should be the main carbohy-drate in a diet because it is easily digested into simple sugars to providequick energy, and it is also high in fibre.

Food

Nutrients

Energy and materials

Carbohydrates, fats, proteins, vitamins, minerals, and water

Growth, development, and repair

provides

in the form of

used for

which provide


www.school.mcgrawhill.ca/resources/Do you know the kinds and quantities of food you

should eat? For information on Canada’s Food Guide, visitthe above web site. Go to Science Resources, then to SCIENCEFOCUS 8 to find out where to go next. Then keep a list

of what you eat for two or three days, and use the informa-tion you found to analyze your diet. What should

you change for a healthy diet?

North Americans tend tohave a low-fibre diet,consuming almost 1 kgof simple sugars (refinedsugar) every week. If youfind this hard to believe,start looking at the labelson cereal boxes, softdrinks, and preparedfoods. Corn syrup anddextrose are examples ofrefined sugars. Refinedsugar not only lacksfibre, it also contains novitamins or minerals.


Despite a bad reputation, fats are essential in our diet. Fats provideus with energy and cushion our vital organs from shock. Unlike carbo-hydrates, however, fats can be stored in the body. When you eat morefats than your body requires, it stores them in special tissues. Once fatcells are formed, they remain in the body waiting to be filled. A properdiet and exercise will ensure that you have enough fat for the properfunctioning of your body, but not more than you need.

Proteins found in foods such as meat, fish, and eggs, are essential for growth and repair of body tissues. In order to obtain all the proteinthat is required, vegetarians must be careful to eat a combination of plants.

In addition to carbohydrates, fats, and proteins, a complete, healthydiet provides all the minerals and vitamins that a person needs.

Disorders of the Digestive SystemThe digestive system consists of many organs that work continuouslyand efficiently to provide your body with all the nutrients you require.Like any body system, it is susceptible to disorders that can arisethrough poor lifestyle habits or disease. For example, why is a high-fibre diet so important? When there is little fibre, it takes the colon alonger time to process waste material (feces). This increases thechances of irritating the colon wall. Over a long period of time, a low-fibre diet may lead to colon cancer. Sometimes the fast pace of life leads people to skip meals, eat too much too quickly at one meal,and eat foods high in sugar, cholesterol, and salt. All of these habitscontribute to colon cancer, but a low-fibre diet is the most importantcontributing factor.

Long-term emotional stress, smoking, or excessive use of alcohol or aspirin can lead to a peptic ulcer. A peptic ulcer occurs when theunprotected wall of the stomach or small intestine is damaged by excess stomach acid. Peptic ulcers can usually be cured by heavy dosesof antibiotics.

As a sports nutritionist, Helga Rempel advises athletes about the effects of thefoods they eat on athletic performance. She knows how the different parts of thebody respond to nutrients such as fats, vitamins, or sugars. She also knows thatdifferent sports require different diets. For example, because of how our musclesuse energy, a marathon runner needs to eat more protein than a weight lifter.

A dietitian is another professional who knows how food affects the body. Talk to a teacher or guidance counsellor about the difference between a dietitian and a nutritionist. Check your phone book, local medical centre, or hospital to find anutritionist or dietitian in your area. Perhaps you could arrange to speak to themabout the work they do. Take notes on your conversation and present your findings in class.

The large intestine con-tains a small fingerlikeprojection called theappendix. The appendixdoes not aid in digestion,but it does contain cellsthat fight off viruses andbacteria. Sometimes apiece of hard fecesresulting from a low-fibrediet can become trappedin the appendix, blockingits blood supply. Whenthis happens, the appen-dix becomes enlargedand may rupture if it isnot surgically removed.

A Healthy Respiratory SystemIf you live in an area where there is air pollution, spend time in buildingswith poor air quality, or sit beside a smoker, you are putting a strain on your respiratory system. Smoking, air pollution, and industrial by-products such as coal dust have been related to many disorders of therespiratory system.

Disorders of the Respiratory System Your respiratory system is lined with cells with cilia, small hairlike projections (see Figure 2.37). These cilia beat continuously to removeairborne particles.

Figure 2.37 Hairlike cilia in respiratory passages trap and remove matter like dirt and bacteriathat enters the passages.

Poisons in cigarette smoke and pollutants irritate this lining, causingmucus-producing cells to produce more mucus. At first, you can removethe mucus by coughing. Over time, however, the irritated lining willbecome inflamed, leading to a condition called bronchitis. Bronchitiscan be treated, but if the irritation continues, the ciliated cells will bedestroyed and the mucus-producing cells will multiply. If this continuesfor a long time, the respiratory airways will narrow and become blocked.Eventually, the bronchitis can lead to a condition called emphysema.Some people inherit this disease, but its major cause is smoking.

Smoking is the leading cause of lung cancer. Lung cancer occurswhen certain compounds in the tar and the smoke contact the lung tissue and cause the cells to grow out of control. Large clusters of these “uncontrolled” cells begin to out-compete the healthy cells fornutrients. The healthy cells are killed, and the cancerous cells continueto divide, leading to cancer.

In the following Think & Link Investigation, you will analyze somestatistics to find out how “deadly” smoking can be.


Working with Statistics

Think About ItCigarette smoking is the most preventable cause ofpremature death in North America. According torecent statistics compiled by the Canadian CancerSociety, tobacco use causes over 40 000 deaths peryear in Canada; cigarette smoking causes about 30percent of cancers in Canada and over 80 percentof lung cancer cases; and lung cancer is the leadingcause of cancer death for both men and women.

What to Do Study the table below.

Source: The National Clearinghouse on Tobacco and Health, Ottawa

Construct a bar graph of the data. Let the x-axis represent the year and the y-axis repre-sent the number of deaths. Use three differentcolours and a legend to distinguish the threegroups of statistics from one another. Giveyour graph a title.

Estimated Smoking-Attributed DeathsCanada, 1965 –1995

1965

1975

1985

1995

12 000

21 000

26 000

31 000

Men

1000

3000

9000

17 000

Women

13 000

24 000

35 000

48 000

Total



2-H2-H

Analyze 1. What is the ratio of male deaths versus

female deaths for each of the years listed?What do these ratios tell you?

2. What is the overall trend of smoking-attributed deaths over these 30 years? Why do you think this is the case?

Extend Your Skills

3. Choose one or more of the statistics fromthis investigation and work with some classmates to make an anti-smoking posterbased on the statistic(s).



For tips on constructing bar graphs, turn to Skill Focus 10.

You and Your BodyWhat would you think if someone advised you tosit on a couch for at least eight hours a day in asmoky room, eat plenty of candy bars, drink lotsof pop, and get no more than three or four hoursof sleep each night? You would probably assumethat you would not feel too well after a few weeks.Your body needs proper care to function properly.However, people sometimes pay less attention tothe health of their bodies than they do to main-taining a bicycle or car.

To maintain healthy organs and systems, everyone has the same essential needs: clean airand water, nutritious foods, exercise, and sleep.

Clean air means oxygen for your cells.Pollution decreases the ability of oxygen to get

into your body. A balanced diet provides your cells with the food materials they need for growth and activities. Lack of essential materi-als weakens the body, while too much of some substances such as fats,sugar, and salt can place a strain on certain organs and systems.

Exercise helps the body process food and oxygen more efficiently. A healthy heart and lungs help carry materials to the cells and get ridof wastes. Strong muscles help protect the body from injury. Your bodyis designed to work, and you feel better when you are active.

Healthy lifestyle habits make you feel better, and they help yourbody resist diseases. Your immune system works more effectively whenyou are well fed and rested. Your immune system attacks and destroysinvading germs and helps break down harmful materials in your body.If you do get a cold, a disease, or an injury, you are likely to recoverfaster if you are basically healthy.

1. Why do humans need a complex circulatory system while an amoeba does not?

2. What can happen if arteries in humans become clogged or narrow?

3. What are the three main types of food? What does each type provide for your body?

4. How do smoke or pollutants in the air affect your respiratory system?

5. Apply When people living in rural India emigrate to a city in Canada,they increase their risk of contracting colon cancer. Explain why.

T O P I C 7 Review




Reviewing Key Terms1. Describe one difference between a vein and a

capillary (6)2. In your notebook, write the correct term to

complete the following sentences:(a) The system transports

dissolved food particles and oxygen. (6)(b) Your body’s responses to stimuli are coor-

dinated by the . (6)

3. What do the digestive system and the respiratory system have in common? (6)

4. (a) Which system in the human body regulates blood composition and gets rid of waste fluids? (6)

(b) Which system exchanges oxygen and carbon dioxide? (6)

Understanding Key Concepts5. Why is such a large percentage of your blood

volume made up of red blood cells? (6)

6. Carbon dioxide is transported through the body in solution in plasma, but oxygen is not.Explain why there is a difference in the waythese two gases are transported by the circulatory system. (6)

7. Suppose you receive a sudden surprise, such as your teacher announcing a surprisetest. Your heart may beat faster and yourbreathing may become irregular. After a shorttime, your breathing and heart rate return to normal. (a) Which two systems are interacting in this

initial reaction? (6)(b) Which system controls and co-ordinates

their interaction? (6)

8. Explain how a fatty diet can affect your circulatory system. (7)

9. What are cilia? How does smoking affecttheir functioning? (7)


Key Termsdigestive systemrespiratory system

circulatory systemalveoli (singular alveolus)

capillariesexcretory system

nervous system


Q How did you become interested in science?

A When I was in high school, I had a terrificteacher of organic chemistry, the chemistry ofliving things. I learned from this teacher thatalthough we can’t always see what is happeninginside our cells, we can still understand what ishappening because of the reactions that we cansee. It’s a bit like looking at the wind — youcan’t see it but you know it’s blowing becauseyou can see the trees moving.

Q When did you begin doing scientific research for a living?

A I completed my bachelor’s and master’sdegrees in biochemistry at the Centre forAdvanced Studies in Mexico City, where I

lived. Then I worked in laboratories runningexperiments for other scientists. Most of the research I did involved studying the membranes of human cells. I was trying tounderstand how materials pass in and outthrough cell membranes.

Q Does your early research have much to do with theresearch you do now?

A Yes. I study one particular kind of protein inthe cell. This is the protein that takes glucosefrom the bloodstream and brings it into thecells of our bodies, especially our fat and muscle cells. This protein is called a “glucosetransporter”. It transports, or carries, the glucose from outside the cell membrane to the inside of the cell.

Diabetes is a disease that affects more than 1.5 million

Canadians. That number is expected to double by the year

2010. Research into how our cells function is being done in

hopes of finding a cure — or at least better treatment — for this

disease. That is where people like Dr. Amira Klip come in. She

is a biochemist and research scientist whose work is known

around the world.

1.

extra glucose transporters

cell membrane

outside cell

inside cell

glucose in blood

2. 3. 4. 5. 6.

Fat and muscle cells have extra glucose transporters inside them. When the hormone insulin signals that there is a lot of glucose in the blood, these extra transporters come to the membrane and let glucose pass through the membrane and into the cell. These diagrams show what scientists think happens as those extra transporters come to the membrane and then return inside the cell once their job is done.

2U N I TU N I T

ExpertAsk an

titleplace type in here

Unit 2 Ask An Expert • MHR 165

Q How does your research relate to diabetes?

A When a person has diabetes, the glucose inthe blood does not get processed by the cells.In our lab, we study how the glucose trans-porter does its job. We try to figure out whatgoes wrong in the bodies of people who havediabetes. We know that people with type 1diabetes can’t produce their own insulin. Theyneed daily insulin injections just to stay alive.Many more people have type 2 diabetes. Forsome reason, insulin doesn’t activate their cellsto process the glucose. If we can find outmore about how the insulin and the parts ofthe cells work together, maybe we can findbetter medical treatment for diabetes.

Q How do you study these cells? Can you observe themwith a microscope?

A It’s not quite that simple. The cell parts westudy are too small to be visible, even with amicroscope. One way researchers study what’shappening is by tagging the glucose trans-porters with something that we are able tosee. That means we attach something to them,

such as a tiny bit of chemical that gives off flu-orescent light. Then we can examine samplesof cells at different points in the experiment.The location of the fluorescence tells us howthe glucose transporter has responded to various stimuli. If the bit of fluorescent lightshows up in the centre of the cell, then weknow that that’s where the glucose transporteris. If the fluorescent tag is at the cell mem-brane, we know the transporter is at the membrane to do its job.

Q Do you spend most of your day at the microscope?

A Not really. I hire research technicians andtrain graduate students to run many of theexperiments. I look at the experimental resultsand try to understand what they mean.

The rest of my time is spent teaching universityclasses and lecturing at conferences all overthe world. Conferences keep me in touch withmy fellow researchers so we can share what we have learned, either new data concerningglucose transporters or new techniques forstudying them.

In this micrograph showing muscle cells, the glucosetransporter proteins have been tagged with a fluorescentchemical so that they appear as bright green spots clusteredaround the nucleus of the cell.

These same muscle cells have been stimulated with insulin for30 min. The highlighted green spots are glucose transportersthat have responded to the insulin and have come to the cellmembrane.

Watch Some Cells at WorkResearchers have developed a technique for videotaping special fat cells cultured (grown) in the laboratory, as they take glucose from the bloodstream. Visit the McGraw-Hill Ryerson website at www.school.mcgrawhill.ca/resources/ tosee some green fluorescent-tagged glucose trans-porters moving about in a cell as they are stimulated.

Search for other Internet sites related to diabetesto find information on the disease itself and tolearn what it is like to live with diabetes. Write a brief summary of the information you find ateach of the sites.


Responding to Changes

Apparatus (per student or group)microscope

medicine dropper

tweezers

depression slide or plain slide

cover slip

Materials (per student or group)Depending on your team’sexperimental design, you may require

• specimens of plant cells (for example, onion skin)

• pond water

• various crystals and solutions

Safety Precautions

• If you use pond water, usemedicine droppers to handle it.

• Do not use animal tissue unless itis a prepared slide.

• Wash your hands with soap andwater when you have completedyour investigation.

Initiate and Plan

With your team, brainstorma number of variables youmay wish to investigate.Choose a manipulated vari-able that is testable with thetime and materials you haveavailable.

Decide on an experimentalquestion to investigate.

Formulate a hypothesis orprediction that will answeryour question. Base this onpast observations, inferences,and research.

Design an experiment to test your hypothesis or prediction. Your design mustidentify the manipulated,responding, and control variables. The steps of yourprocedure must clearlyexplain how the experimentwill be carried out. Use diagrams to help explain theprocedure if they will help.(You might find it helpful torefer to the ExperimentalDesign Checklist on the next page.)

S K I L L C H E C K





Think About ItCells, either as a part of plants and animals, or existing alone as a micro-organism, are always part of a larger system. They are influenced by changes within the cell, and also by changes outside the cell. This means that environmental changes may affect their functioning.

What would happen to the plants in your garden if they were exposed tosalt water instead of plain water? What happens to micro-organisms whensnow and ice from salted roads melt and run into rivers and ponds, or whenoil that drips from vehicles is washed down storm sewers?

In this investigation, you will work with a team to explore the responses of cells to specific environmental changes.

Share your design with yourteacher and other classmatesfor feedback. Make anychanges necessary to yourdesign before you proceed.

Perform and Record(Test Your Hypothesis)

Set up and perform yourexperiment. Modify yourdesign if necessary. Carryout two or three trials toverify your findings.

Gather and record data andobservations. Decide how torecord and present your datain a clear format (table,graph, diagram, etc.).

Write up a laboratoryreport. Be sure to include allthe parts of the report, alongwith diagrams or drawings.

Analyze and Interpret(Draw Conclusions)

Draw conclusions based on the results of your experiment. Discuss yourconclusions with your team.

Was your hypothesis/predic-tion supported? If so, whatevidence supported it?

Unit 2 Design Your Own Investigation • MHR 167

Experimental Design Checklist1. Have you stated the purpose of your experiment (the

question you want answered)?

2. Have you written your hypothesis or prediction about whatyou expect the answer will be?

3. Have you obtained all the information you need from a variety of sources to design your experiment?

4. Have you made a complete list of all the materials you willneed?

5. Have you identified the manipulated, responding, and controlled variables?

6. Have you written a step-by-step procedure?

7. Have you re-evaluated your experiment to look for errors inits design?

8. Have you repeated your experiment several times? Were theresults the same each time?

For tips on designing an experiment,turn to Skill Focus 6.

Review2


U N I TU N I T

Unit at a Glance• All living things are made from cells.• Living things need energy, respond to their

environment, reproduce and grow, and produce wastes.

• The invention of the microscope allowed scientists to see and study the structures andfunctions of cells.

• All cells, whether in unicellular or multicellularorganisms, carry out similar functions.

• Organelles are the structures within cells thatenable them to carry out activities necessary for life.

• Plant and animal cells have a cell membrane, cytoplasm, a nucleus, and vacuoles in common.Only plant cells have cells walls and chloroplasts.

• A cell membrane is selectively permeable because it allows only certain substances in andout of cells.

• Diffusion and osmosis are the processes bywhich substances move through cell membranes.

• Cells are specialized to perform particular tasks,and their structures are related to their functions.

• Cells with the same structure and function aregrouped into tissues; groups of tissues formorgans; organs work together in systems.

• Plants have three systems: a root system, a shootsystem, and sometimes a reproductive system.

• The two tissues that transport nutrients in aplant are phloem and xylem tissues.

• In humans, the digestive system provides foodfor the cells, the respiratory system supplies oxygen and gets rid of waste gases, and the circulatory system distributes food and oxygenand carries away wastes through blood.

• The excretory system filters waste material from blood.

• The nervous and endocrine systems work togetherto co-ordinate the body’s responses to stimuliand provide a stable environment for cells.

• Our bodies need clean air and water, nutritiousfoods, regular exercise, and sufficient sleep tomaintain healthy organs and systems.

Understanding Key Concepts1. Make a drawing of the microscope shown and

label its parts.

2. Describe how to prepare a wet mount. You may show the procedure in a diagram.

3. Explain why cells are considered to be living systems.

4. Make a labelled diagram of a cell showing the structures both plant and animal cells have in common.

5. Which part of a cell allows it to exchange substances with its surroundings?

6. Write a definition of (a) diffusion, and (b) osmosis.

Unit 2 Review • MHR 169

7. How does the particle model help us to under-stand how substances move in and out of cells?

8. Explain how (a) animals and (b) plants obtain carbohydrates.

9. Explain how the structure of a specialized cell is related to its function in the body of a multicellular organism.

10. Identify the specialized cells shown. Describehow each cell is suited to its role.

11. Explain the function of each of the three systems of a plant.

12. Describe the process by which water (a) entersa plant and (b) leaves a plant.

13. What effect might pruning (trimming) a tree’sbranches have on the transport of water up thetree trunk?

14. Why is a plant growing in the shade less likelyto wilt than one growing in sunlight?

15. List five body systems found in humans.

16. Copy the letters from the diagram below intoyour notebook. Beside each letter write the correct term.

17. Name the organs in which substances passbetween the circulatory system and (a) the respiratory system, (b) the digestive system, (c) the excretory system.

A B

F

G

E

D

C


Developing Skills18. Draw a Venn diagram like the one shown.

Where the circles overlap, list characteristicsthat living things and non-living things have incommon. In the left circle, list characteristicsshown by living things only. In the right circle, list characteristics shown by non-livingthings only.

19. Suppose you are studying a slide of plant cells.You count 40 cells in a row across the diameterof the field of view. Make a flowchart describingor showing a technique you can use to estimatethe average size of each cell.

20. The table shows the results of an experimentto find the effect of osmosis on potato cells.Two cubes of potato were weighed and placedin distilled water, and two cubes were weighedand placed in salt solution. The mass of eachpotato cube was determined at 15 min intervals.(a) Calculate the average mass of the cubes in

the water and the average mass of thecubes in salt solution at each time interval.

(b) Plot the data on a graph, showing averagemass along the y-axis (the vertical axis), andtime along the x-axis (the horizontal axis).

(c) Briefly interpret the results. What has happened to the mass of potato in water?What has happened to the mass of potatoin salt solution? Why?

21. These two sets of data represent the heartrates of 30 individuals — 15 athletes and 15non-athletes — after 10 min of intense physicalactivity. The sample frequency table shows thenumber of athletes in five different heart rateranges. Follow this model to make a frequencytable for the non-athletes. Compare the datain the two tables. What can you concludeabout the effect of physical training on heartrate? How could you display the data to makeit easier to analyze?Heart rates of 15 trained athletes after physical activity: 128, 131, 120, 127, 132, 125,129, 122, 127, 133, 135, 130, 123, 128, 124Heart rates of 15 non-athletes after physical activity: 143, 139, 144, 132, 138, 135,141, 137, 128, 139, 140, 136, 133, 143, 135

Sample Frequency Table Heart Rate of Athletes after 10 min of Activity

119–122

123–126

127–130

131–134

135–138

Range of heart rates

II

III

IIIIII

III

I

Tabulate data

2

3

6

3

1

Total number of athletes in range (frequency)

Livingthings

Non-living things

Commoncharacteristics

Cube 1mass (g)

Time(min)

Cube 2mass (g)

Average(g)

Cube 1mass (g)

Cube 2mass (g)

Average(g)

Salt water Distilled water

0

15

30

45

60

59

58

50

50

50

60

58

55

54

53

51

51

52

53

55

52

52

53

54

53

Unit 2 Review • MHR 171

22. Make a concept map to show how the follow-ing are related in humans. Link the conceptstogether using a few key words or descrip-tions. Add any other terms you need.food external environmentoxygen lungssmall intestine cellscirculatory system carbon dioxide

Problem Solving/Applying23. Imagine you are exploring another planet

and you find a small, green, leaf-shaped objecton the ground. How would you tell if it was a living, alien organism or part of the non-living world?

24. Explain why animals and plants are made ofbillions or trillions of microscopic cells ratherthan a few large cells. You may use a diagramin your answer.

25. Suggest what adaptations might be found in(a) the leaves and (b) the roots of a plant livingon the tundra, where conditions are cold anddry. Give reasons for your ideas.

26. Design Your Own Why might a plant wiltin hot weather? Why might a different plantnot wilt in hot weather? Design your ownexperiment to compare the responses of twodifferent kinds of plants to an increase in temperature. Write or sketch the steps of your procedure.

27. The normal breathing rate of an infant isfaster than that of a teenager. Why do youthink this is so?

Critical Thinking 28. Suppose a new disease destroys chloroplasts

in plant cells. Explain what would happen to(a) the plant cells, (b) the plant, (c) other formsof life.

29. A friend tells you that people and trees are completely different forms of life. Explain why you would agree or disagree with yourfriend’s comment.

30. Why will a goldfish die if it is placed in salt water?

31. What problem might athletes face if theydrink only distilled water after a race? Explainyour reasoning and suggest how the problemcould be avoided.

32. Three items that you cannot live without arewater, food, and air. Why does a lack of airlead to death much faster than a lack of theother two items?

33. When you exercise on a hot day, you sweatand become thirsty. Explain how sweating andthirst are examples of your body’s response tochanging conditions.

In your Science Log, write about the things you are doing orshould be doing to keep your body healthy and functioning properly. Explain why these things are important using whatyou have learned about cells, tissues, organs, and systems.

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